PC will not boot up completely. Stuck on POST screen. Please help

[szetop]

The problem happens suddenly. Was working fine before. Don't recall installing any new software. On switching the PC, sometime display will appear on monitor. Other time nothing. The time when the display appears the last message is "Memory testing : 524288K OK". Cannot go into BIOS setup, even on pressing the DEL key. Used to work before.

My setup:
Gigabyte GA-8I915P Pro
Intel Pentium 4 3GHz
3 SATA disks
2 DVD/CD
Antec PSU Truepower 2.0 480watts
Gigabyte X600 Pro 128D

Please help.

 

[szetop]

Further details to above problem. On pressing the reset button, the monitor goes blank. Nothing appears. On cold boot again, after a couple of minutes, nothing appears, no beep either. However if I leave in off for say 2-3 hours, display comes back on again and the computer stuck at the same point. I'm really in deep sh##, am I? Please, please someone helps. Don't want to spend any more money. PC is only about 13 or so months old.

 

[kirock]

Unplug everything except your OS HDD, RAM and video card. This means the data cables and the power connections. Reseat your video card and RAM. Reset your CMOS, see mobo manual for procedure. Usually a jumper on the mobo or a pb switch.

If not try running with one stick of ram and as above.

 

[szetop]

kirock, I had done all of them earlier. No good. Had even tried reconnecting back the old power supply. The only thing I haven't tried is to reseat the whole mobo. If only I can access the backup CMOS, (giga has 2 bioses). With the OS HDD left on, a message appeared on scree, indication that a checksum error with the CMOS and that the default will be loaded. The keyboard then froze once I enter the BIOS setup. Cold boot again. Blank screen appeared, no bleep from the PC. Guess I'm going to leave it till the next day. Will keep you post. Meanwhile anyone elase has any idea?