when i turn on my computer the only thing that starts is the fan, nothing shows up on the screen. I then try to turn of the pc by pushing the off/on button but it does not respond, it still stays on. The only way to turn of the computer is by unplugging it.

Can you get into the BIOS as it boots up by pressing the appropriate key (sometimes F2 - refer to the manual)?
Are there any beeps from the PC ? If so, how many and at what interval?
Are you holding down the off button for at least 5 seconds or just pressing it once?
Sorry for so many questions but it's just to get a better idea of what's going on.
There are many things that it could be - top favourites are the graphics card and/or motherboard

thank you for your response, but now i have another problem. i opened my computer and i moved a wire from the power supply and that seem to fix the problem, but now when i turn it on, my keyboard and mouse don't work, i then push the off button and instead of turning off it goes into hybernating.