Sometimes it works, sometimes it doesn't

[ankhev]

Hi there. Hope someone can help with the following problem:
Computer was working fine until recently and I haven't made any changes or added any new hardware. When I switch it on it powers up with fans running and lights on etc but there are no beeps and nothing on the screen, no lights on the keyboard and the broadband modem light just flashes. However if I switch the power off at the mains and back on again and then try again it usually comes on and everything works fine after that (sometimes I have to do this two or more times to bring it back to life). Its an Athlon XP2400 running windows xp. 512mb ram. Graphics is onboard. As I say, had no problems at all for the last 3 years apart from replacing the psu about a year ago.
Any ideas what could be wrong?

 

[SYL\X/3K]

read this sticky : http://www.techist.com/showthread.php?s=&threadid=127815

i had exact same problem with my old Athlon xp, i had to switch the back switch off and then back again to at least POST because i had RAM problems but stupid me kept on on reseting and restarting it thousands of times that i killed my mobo and left me a burn mark on the 20 pin power plug as well as my mobo as a souvenir.

 

[ASMOTH]

If your ATX connector ( That's the 20/24pin lead of your PSU ) isn't seated properly your computer won't pass the P.O.S.T test at boot, pressing reset or hard-braking ( turning on and off the PSU switch ) will by-pass P.O.S.T, but can do some real nasty damage to your machine. Try this.