My computer regularly crashes when playing games, this usually occurs anywhere between 5 and 30 minutes though on the odd occassion it will last longer.
The usual symptoms are that the screen freezes for a while then the screen goes blank. The PC has to be restarted.

I have checked the System Requirements Lab (stickied in this forum) and all the games I have tried return as Passed.

Specs are:

Processor: AMD Sempron(tm) 2400+, MMX, 3DNow, ~1.7GHz
Memory: 1024MB RAM
DirectX Version: DirectX 9.0c
Graphics Card: CONNECT 3D RADEON 9550 (256 MB)

Can anyone assist with my problem? Is there anymore information that is needed?

Found your problem already boet. Its your graphics card. Update your drivers. If not make sure you have the latest verion netframework 2.0. But the problem is def your card. Also check if you have fastwrite enabled or disabled.

What games are you playing on it?

Initially problems were with World of Warcraft and then Warhammer: Dawn of War.

I updated the Graphics and sound drivers and Dawn of War played through for an hour and a half with no problems. I had updated the Drivers previously and the problem persisted but there had been a new one since the last time I updated.

Hopefully thats the problem sorted but only time will tell.

If the problem isn't solved, open your case and tell us how many watts your power supply gives, and how many Amps are on the 12v Rail. If you don't know how to get this information, take a picture of the power supply sticker and post it here.

Well of course I jinxed it by speaking too soon and the problem persists.

So far I have:
Updated Graphics and Audio Drivers
Disabled Fastwrite
Enabled Fastwrite

I have not yet applied any game patches.
I have tried Dawn of War after each step and the error as described above occurs again.
I couln't get a photo of the power supply at the moment but the details off the label are :

Model JNP-350p
AC INPUT: 115v 8A
220-240v 4A
Frequency: 50-60 Hz
Peak: 350W

DC Output
+5v 3.3v +12V -5V -12V +5VB
30A 28A 16A 0.3A 0.8A 2A
180W MAX 192W 1.5W 9.6W 1.0W

hope that helps.

Thanks everyone for your help so far.

Update:
I ran SpeedFan which gave CPU temperature readings of 61C at idle.
I opened the case to clear any dust out and booted with the case open and noticed that the small fan over the motherboard processer didn't start. I nudged it with the handle of a paintbrush and it started. I am now getting idle readings of 51/52C.
The same error occured when running Dawn of War.
I have rebooted with case open to ensure this fan now boots up and it does with the same readings as above (51C) but the error persists.

I don't know if now you've fixed it the temp is ok for your proc, I just guess semprons might run at such a high temp, but the first thing that came into my mind when i read your first post has been: this guy is suffering from high temperature. I had a problem like your in the past years and the only way i could run 3dgames was putting a fan in front of my open case, specially on summer . I'm much more concerned about cooling since, as it is most important to keep your hardware as cool as you can.

It has a fanless heatsink

The PSU died today and is currently replaced with a 400W Jeantech.

The same crashing prblem occurs.

NOt sure which of the voltage information is relevant so I've just put it all.

NB: 1.63V
CPU CORE: 1.62V
DDRVDD: 2.63V
3.3V: 3.33V
5V: 5.12V
12V: 12.23V
AGPVDDQ: 1.59V
DDRVTT: 1.32V
5VSB: 5.14V
VBAT: 0.00V
3VDUAL: 3.30V
GMCHVTT: 1.63V