Dannyg154

hi i have a big problem with my pc and its driving me crazy, it all started when i updated all my drivers, then when i was trying to play a game, e.g world of warcraft the computer would freeze, then unfreeze and freeze again and keep doing so until i turned the computer off. then the problem deteroriated and the pc would turn itself off on boot but the psu fan carried on running so the only way to turn off was to unplug, but if i tried to boot about 5 or 6 times it eventually came on, but now i turn the pc on and the cpu fan and psu fan kick in then after 5 secs the cpu fan turns off along with the mainboard, but again the psu fan carries on, but no matter how many times i try i cannot get it to boot, i tried unplugging the cpu fan which gave no joy, swapped the memory, unplugged and replugged all mainboard components cleared all dust from the machine and still i get the same problem, i replaced the psu about 7 months ago, but it was replaced with a 2nd hand one and i fear that may be the problem, please can you tell me what the problem is and what parts if any i need to buy

p.s the computer is a emachines 5220, p4 2.6ghz, 1gb ram 80gb hdd and 128mb ati radeon graphics card

thanks a lot for the help my email is dannyg154@hotmail.com