Wont boot up

[Cookieboro]

I built a computer useing the below hardware and it ran fine for the full setup of windows and installtion of misc utilities. Then i rebooted and use it for about 1 hur to check it was running fine. But 1 day later it seems to have stoped working. When i press the power button the full system starts up but the screen dose not come on. i managed to get it on one time but no more luck. i set the jumpers for the cpu to 333mhz and showed xp2500 on the bios.
Dose this sound like i set somthing up wrong or should i be sending for replasment parts from the computer shop?

ASROCK K7 SIS 741 GX+
AMD ATHLON XP2500+ OEM BARTON
MAXTOR 80 GB 7200/133
LITEON 52X32X52 CDRW RETAIL BOXED
ADVANCE PSU 400 WATT ATX
E-machine Bare Bone Case, Keyboard & Mouse
256MB DDR RAM 266 Mhz PC 2100 184 Pin
Mentor K7-30 Copper Cooler Fan XP3000
GEFORCE FX 5200 128 MB AGP 8X

 

[Praetor]

Then I rebooted and use it for about 1 hur to check it was running fine. But 1 day later it seems to have stoped working

Check voltages and memory.

i set the jumpers for the cpu to 333mhz and showed xp2500 on the bios.

Is is supposed to be clocked like that?