Computer has strange problems, then crashes

[AtariPlayer]

My computer is a Windows XP desktop, I think made in 2003. It is from some off-brand called North Star. Last month, I was playing a 3D game on it when suddenly, anomalies appeared on the screen that looked like small, multicoloured pixely smudges. Meanwhile, the computer hung. I waited a few minutes and rebooted it a few times, and it booted on the 3rd try. After that, around 10-40 minutes of being booted, the same problem would happen again, only this time, one of four things happened:
1.Same as last time; screen anomalies.
2.Screen would go completely black (computer ceases to send information to the monitor).
3.Screen would simply freeze.
4.Entire screen would get covered up by a random-coloured, pixely texture.
After several days of this, the computer now refuses to boot. When I turn it on, all the lights come on, the hard drive does something then stops, all fans come on, and the CD drive checks for a CD. Also, it does not beep like usual, and the screen is black.
Yesterday, I tried it to see if it would work. Something different happens now: when the computer is first connected to power, it will turn on, then shut down for exactly 5 seconds, then turn back on and have a black screen again.

Please help, I have no idea what is wrong with it. I did back up the data I needed the most when it was still working.

EDIT: I just noticed, upon startup, for a few seconds the power light blinks.

 

[Tiago Arlan]

your hard drive may have failed..check your BIOS if it can see your disk..if not,replace disk.if yes,check Graphics Card inside BIOS if its connected..graphics card may have a problem..

 

[AtariPlayer]

your hard drive may have failed..check your BIOS if it can see your disk..if not,replace disk.if yes,check Graphics Card inside BIOS if its connected..graphics card may have a problem..

Cannot check the BIOS, the computer will not boot at all, just stays at black screen when started.

 

[Tiago Arlan]

do you mean it just reboots itself without showing POST msge??..follow advice anonymous1, you may have a shortage in your PSU..

detach PSU and check output voltages,if cant handle it,better replace.