I have a Dell Dimension 8250 running XP that will not boot up.
The power indicator (small green light) on the motherboard comes on when the power cord is plugged into an electrical outlet but when I press the "ON" button nothing happens.
Using a volt meter, I have checked the power supply and everything seems to be okay.
I jumped the "power supply on" circuit and the power supply fan ran.
Is there any test that I can run to rule out the "ON" switch being bad?

Any suggestions or other tests will be greatly appreciated.

Thanks

You cannot reliably or conclusively test a PSU with a multimeter. If not connected to the motherboard, it is not properly loaded, and multimeters do not properly test for unwanted AC components in the DC.

How did you jump the PSU to turn it on? If by shorting the two motherboard pins, that is the same thing as pushing the case's front panel power switch.

Here is my canned text on testing PSUs.

To properly and conclusively test a power supply unit (PSU), it must be tested under various realistic "loads" then analyzed for excessive ripple and other anomalies. This is done by a qualified technician using an oscilloscope or power analyzer - sophisticated (and expensive) electronic test equipment requiring special training to operate, and a basic knowledge of electronics theory to understand the results. Therefore, conclusively testing a power supply is done in properly equipped electronic repair facilities.

Fortunately, there are other options that are almost as good. I keep a FrozenCPU Ultimate PSU Tester in my tool bag when I am "in the field" and don't have a good spare power supply to swap in. While not a certain test, they are better than nothing. The advantage of this model is that it has an LCD readout of the voltage. With an actual voltage readout, you have a better chance of detecting a "failing" PSU, or one barely within specified ATX Form Factor Standard tolerances. Lesser models use LEDs to indicate the voltage is just within some "range". These are less informative, considerably cheaper, but still useful for detecting PSUs that have already "failed". Newegg has several testers to choose from. All these testers contain a "dummy load" to fool the PSU into thinking it is connected to a motherboard, and therefore allows the PSU to power on, if able, without being attached to a motherboard - great for testing fans, but again, it is not a true load or suitable for conclusive testing.

Note the required voltage tolerance ranges:

NOTE: Disregard the -5VDC reading. It is no longer used.

Swapping in a known good supply is a tried and true method of troubleshooting used for years, even by pros. If you have access to a suitably sized, spare power supply, carefully remove the suspect supply and replace it with the known good one, and see if the problem goes away.

I do not recommend using a multimeter to test power supplies. To do it properly, that is, under a realistic load, the voltages on all the pins must be measured while the PSU is attached to the motherboard and the computer powered on. This requires poking (with some considerable force) two hard and sharp, highly conductive meter probes into the main power connector, deep in the heart of the computer. One tiny slip can destroy the motherboard, and everything plugged into it. It is not worth the risk considering most multimeters, like plug-in testers, do not measure, or reveal any unwanted and potentially disruptive AC components to the DC voltages.

Note the ATX Form Factor standard does not "require" specific color coding for power supply connector wiring. It has recommendations but manufacturers often do not follow them. Sadly, many testing guides or tutorials will refer to wire color only and that can lead to improper testing.

The voltages can be checked in the BIOS Setup Menus of most motherboards but they do not reveal ripple or other anomalies either. And of course, booting into the BIOS Setup Menu requires a working PSU.

As always, before working in the interior of the computer case, take necessary ESD precautions to ensure static buildup in your body does not discharge through and destroy any sensitive devices. Unplug from the wall and touch bare metal of the case before reaching in. And remember, anything that plugs into the wall can kill. Do not open the power supply's case unless you are a qualified electronics technician. There are NO user-serviceable parts inside a power supply. If you do not have a tester or a suitable spare to swap in, take the PSU to a qualified technician for testing.

For more information on testing PSUs, see this excellent article by Gabriel Torres, Why 99% of Power Supply Reviews are Wrong.

I unplugged the ATX connector from the motherboard and using a piece of wire, I connected the green wire on the ATX connector with a ground wire, and the fan ran.

I did not have a good feeling about this test because the voltage could be inadequate on any of the other 17 wires.

The only other test that I tried was removing or unplugging everything in the computer and pressing the "ON' button until the green light on the motherboard went out. I then plugged in the power cord, pressed the "ON" button and listened for beeps.

I am going to try another known good power supply.

I am going to try another known good power supply.

Sounds like a plan. Keep us posted.

I tried a identical Dell power supply that is known to be good without and change in problem.

Any suggestions will be appreciated.

No beeps? When did this problem first surface?

No beeps..

I was out of town and the utility company replaced my electric meter.

It is possible that a surge of power occurred and took out the motherboard.

This computer was not protected by a surge protector.

It is not likely replacing the meter did anything, unless, perhaps, the computer was running when they pulled the old meter. After that, the power should have been off and a surge would have to be huge - like from a nearby lightning strike - to make it past the PSU and hit the motherboard. If swapping the meter did anything, I would expect it to affect only the PSU.

That said, electricity does not alway follow logic or theory as we expect, so I say "not likely", but not impossible.

With two PSUs giving the same indications, it does not look good. Do you remember if there ever was any beep? Typically, when all is well, if there is an internal "system" speaker you would hear a single beep during the boot process that indicates POST (power-on self test) completed successfully.

If me, I would pull all but one stick of RAM and boot with that. I would also swap in another graphics card - though most people don't have extra cards laying around like I do.

You should probably also consider pulling the drive(s) and installing it into an enclosure, or into another computer as a secondary (NOT boot) drive, then copy off any files you don't want to lose.

Note that I am not a fan of surge and spike protectors. IMO, they are little more than fancy and expensive extension cords. Instead, I recommend all computers be on a "good" UPS with AVR - automatic voltage regulation. These are commonly called "battery backups" but backup power during a power outage is only their secondary benefit; it is the AVR that makes beneficial, if not essential.

I pulled all of the memory except for one stick, no sounds.
I replaced the video card, no sounds.
The only thing that indicates life is the small green light on the motherboard.
I have not replaced the battery. Is it possible that could be the problem?

Typically, the light on the motherboard only indicates the power supply is providing the ATX required +5Vsb standby voltage - a reminder to unplug before pulling or inserting RAM.

A bad or dead motherboard battery would like just cause your system's date and time to reset and may force you into the BIOS Startup menu. But I don't see how it would cause the system to not boot - they are inexpensive so trying a new one would not break the bank. You can get them at most camera/watch/battery counters. But I fear your motherboard or CPU, or both, is toast. And unless you have a spare CPU laying around you can risk sacrificing, I am afraid your options are limited to taking the computer to a shop, or start budgeting for a new computer.

Sorry I don't have better news.