Hey, this monday night my computer randomly turned off and wouldent boot at that time. I just assumed it was a overheat issue since it happened once before and thought it would be fine in the morning. However I was sadly wrong. Whenever i try to start my computer either it will just shut down 5 seconds after I press the power button or will get me to windows but will shut down before its done loading the desktop.

Brought it to tech who did a quick check over it. Tried a differnt power supply, blew out all the dust, took the ram out and tried it with only 1 stick etc, however the problem still occured. He said it was most likely the motherboard or processor and possbily but unlikely the ram. Also, when I brought the tower back home and it being unplugged for about 6 hours it loaded the desktop and stayed on for about 3 minutes before shutting down (i was able to aceess and run programs fine), after which it would keep shutting down 5 sec afters boot up. Just wondering if anyone has any ideas how to fix this and if it is a fan problem or the processer or motherboard is fried or damaged. Also I did try differnt cables, power outlets and power bars as well.

I would download and run memtest86 from a bootable floppy to rule out a memory error.
http://www.memtest86.com/

"Brought it to tech who did a quick check over it."
Sure hope you didn't pay this "tech" for his service.
Things to try: Disconnect all hard-drives and optic drives and floppy drive. (remove both power and data cables).
remove any extra plug-in cards. Leave only one stick of ram and graphics unless you have onboard. Now connect power and see if you can boot into bios. Check system health and see if there is an overheating problem. If the system is stable in barebones configuration then add back one extra device at a time(disconnecting power between each change) until you identify the problem.

If it won't run in barebones mode then your problem is with either powersupply, motherboard, CPU , ram or graphics, and without spares to swap in/out you may not be able to identify exactly what.

Post back after you've tried some of this and let us know the outcome.

I used to have a signature but it disappeared and I just couldn't be bothered writing another so please feel free to ingore this.

Either your power supply is on the way out or your CPU is overheating.

Tried it in bare bones with a new power supply and using onboard/different video cards, all of which didnt work. Will try doing the memtest once i get back, thanks for the responses so far.