I have a Pentium 4 PC that I run XP on.

It has been crashing when I play games, but it was fine installing windows and games. The crashes are as if I pressed the reset button ony my PC, no locking up or BSOD. Quick specs:

ECS L4A8S2
Pentium 4 2.4B GHz 533MHz FSB no HT (can't remember which code that is)
1024MB + 256MB DDR400 RAM
GeForce 6600LE
WD 160GB IDE

I got the following "an serious error occured message" when I reset the PC.

BCCode: 10000050
BCP1: FFB1E937
BCP2: 00000000
BCP3: FFB1E937
BCP4: 00000000
OSVer: 5_1_2600
SP: 3_0
Product: 256_1

Memtest managed 2 passes whilst I was doing chores this morning.
HD Tune did an error scan with no bad blocks. The Info and Health tabs list everything as OK.

This leaves me to suspect either power supply or graphics.

Power supply: One of the molex connectors is a bit broken I think. My PSU is modern and only has 2 molex + floppy on a single cable. If I plug CD and HDD into 1 and 2 respectively (where 1 is closest to the PSU), it won't detect the HDD in POST. If I reverse the order, it is detected without issue, but clearly there are some power issues going on!

GPU: I took the heatsink off and cleaned it up. The heatsink, card and mounting kit are all not exactly straight so it is possible the heatsink isn't making good contact with the GPU but it looks fine to me. Also my board is very fussy about how the GPU is inserted and I sometimes need to re-insert the GPU into the AGP slot a few times for it to work (but when the crash happens and the PC reboots it doesn't beep saying no GPU detected.

So power issue or GPU issue?