Really, someone with a lot of experience should help me out, because what's happening to me is rare. No, I'm not trying to get attention, I'm serious.
Here's the problem, please read...:

First to let you know, my parents are divorced, so when I'm speaking about my dad, I'm in an other house then my mother's
Believe me, that's important to know.

When I'm using my own pc (I'm on someone else's now) it crashes. Sometimes after weeks, sometimes days, sometimes even hours. First time it crashed my mother board and graphics cars were destroyed. My dad got a new ones, installed them, and my pc worked fine again. That time we didn't knew the problem yet...

Few hours later (when I was home again, with my mother), it crashed again, resulting in a destroyed graphics card only. Mother board still working fine... We went thinking about some agressivee virus, though I have perfect AntiVirus software and everything else running. We thought so because I downloaded some game just before the first crash.

But virusses dont destroy motherboards + graphics cards...

Again he bought new graphics card, installed it, everything working fine. 10 days later, I was home again with my mom, it crashed. So I took it to my dad again, but there it was still working. Nothing destroyed. I used it there several days playing games 'n stuff, but it kept running...

Now it's still with at dad's house, cuz we don't know wtf is wrong. It could be something with my monitor, like it's sending sometimes a little high voltage, but we don't know... Someone told us it could also something with my elektricitysupply... (cant explain in english)

We are sure that it is NOT:
- Virus
- Any hardware inside the pc
- Any software

Comments please?

First off, with all due respect, I wonder how you know that these pieces of hardware were "destroyed". Did they catch fire and burn?

Or are you assuming that since the computer was not working that the hardware was "destroyed"?

Next:

1) By crash do you mean the computer completely powers off by itself?

2) Are you sure all your hardware is compatible?

3) When you changed motherboards did you Clean Install the operating system and add all the motherboard drivers?

4) Are you using a surge protector?

5) Have you tested the PSU? Or tried a new one?

6) Do we understand that the computer is running now after its' last "crash"?

I called it destroyed... it's just broken/not working. We've tested it...
We took out the 'broken' graphics card and put in some other old one, and my pc worked fine. Also, the 'broken' graphics card doesn't work in my dad's pc anymore... That's how we concluded that it was broken (same way with the mother board)

1 - The screens just suddenly turns black, but the computer seems to be still running. Once turned off, it can't be turned on again.

2 - Yes, I'm sure...

3 - Complete installation, yes

4 - What's surge protector

5 - There's nothing wrong with it...

6 - Yes, it's running fine now, but it's at my dad's house, cuz once I bring it here it might crash again. At my dad's it's just running fine...

is the power bar power surge protected, or are you just plugging directly into wall? I would check the AC voltage on the AC outlet to be perfectly safe, might need a Hydro meter tester to test for Open Grounds or Hot grounds. If you have a Hot ground, it can cause my problems, I was at a subscribers house one day and plugged something in, and literally the device i plugged in burst into flames because of the "hot" ground on the AC outlet. Just another avenue to look down, sometimes its good to think outside the box.

you would think though that if it was a hot ground or power surges that it would fry the PSU as well as the mobo. I could be wrong on that though. I would check the PSU, it may be sending to much voltage through the system. it might help to know exactly what kind of system it is here, brand of mobo, vid card, etc. Id say make sure you have a good surge protector (its a long bar with lots of plug ins with a cord on the other end that plugs into the wall) and plug everything into that, and you might try swapping in a new PSU. that may help.

Well, it seems to me if the computer works fine at your dad's house but not yours, then I would expect something with the power, either the house current (mains) or your power supply unit (PSU) - I think this is what you are calling your "elektricitysupply". Unless the voltage at your house is abnormally low, I would not expect this to be an issue with house current - for example, yours reading 107VAC instead of at least 110V.

It could certainly be lousy (and unsafe!) wiring in your house and that should be checked. At the very least, EVERYONE should have an AC Outlet/Ground Fault Indicator Tester. There are testers for every type (country and voltage) power outlet. Visit your local home improvement store. Then test all outlets in your house - especially the kitchen and bathrooms.

The fact that it works at your dads could also simply indicate a loose connection that was jostled during transport.

When you replaced the motherboard, were you 200% certain you put motherboard standoffs only where the motherboard had a corresponding mounting hole? This is critical! Cases are designed to support 1000s of motherboards, therefore they have more mounting holes than most motherboards need. A standoff under the motherboard where no mounting hole exists can destroy the motherboard, and anything attached to it, by shorting critical circuits the time power is applied.

Also, did you use TIM (thermal interface material) when mounting the CPU's heatsink fan (HSF) to the heatsink? This too is critical to ensure the CPU does not overheat.

Other things to consider - ambient (room) temperatures affect operating temperatures of the components. If your house is warmer to start, it may be overheating, but staying cool and stable at your dad's.

you would think though that if it was a hot ground or power surges that it would fry the PSU as well as the mobo. I could be wrong on that though. I would check the PSU, it may be sending to much voltage through the system.

Actually PSUs are pretty robust and can generally take a lot of abuse, from the power source. An underpowered PSU, on the other hand, can fail, and damage connected components. Unless there was a severe power hit, in which case I would be wondering about TVs, other electronics in the house too. Still, PSUs do go bad, so it is still a good idea to check it out.

Of course, EVERY computer system (and any other high-tech - expensive electronics) should be protected with a good uninterruptible power supply (UPS). A surge protector is nothing more than a fancy and expensive extension cord! An UPS is often called a battery backup, but backup power is only a minor function of a good UPS. A "good" UPS comes with AVR, automatic voltage regulation. AVR provides MUCH greater protection over even the best surge protectors because it regulates or conditions the power.

A surge and spike protector merely chops (clamps) off the excess voltage (until they overheat and fail). An UPS w/AVR uses intelligent electronics to almost instantly lower the voltage if too high, and raise the voltage during power dips (opposite of spikes), sags (opposite of surges), brownouts (an extended sag). Raising low voltage is something no surge and spike protector can do.

And it is important to note that ANY TIME a high wattage appliance (washer, oven, toaster, refrigerator, coffee pot, electric clothes dryer, hair dryer, vacuum, etc.) cycles on and off, spikes, dips, surges, and sags are sent down the line. If you have any like electrical device in your home, apartment, or office building, you need a good UPS with AVR.

might need a Hydro meter tester to test for Open Grounds or Hot grounds.

Ummm, a hydrometer measures "specific gravity" in liquids (hydro, a prefix meaning water), such as beer, alcohol, or electrolytes in batteries. A multimeter or VOM (volt-ohm meter) would be used to measure a circuit for shorts, opens, and voltage.

like i said i could be wrong about the PSU failing under poor voltage. and i think thats what the guy meant when he said hydro filter you ever do that? think one thing and say another? lol.

Sure - like you meant to say hydrometer and instead you said hydro filter! lol

lol ok i just went and did it to so sue me :P you wont get much. see what happens, i stick up for someone and it happens to me! rotfl

As Digerati says, just moving a PC from one place to another can cure (or break) poor connections on cables, graphics cards, etc. Just this week, I fixed a customer's PC that kept freezing every few seconds by simply driving it 4 miles to my office, running the PC for 12 hours and then driving it back to the customer's office. It works OK now!

I would definitely get a power supply tester on the PC's internal power supply unit (PSU) - these can be obtained cheaply through Ebay. But, more than that, I would agree with the suggestion already made that there could be a problem with the electrical wiring or sockets at your mother's house. Scary!