Desktop

It's sounds more like your CPU is overheating, 250w power supply is more than enough.

Check your motherboard manual & see if it mentions any utilities for monitoring your temps & fan speeds. Or go to their web site & check for any.

If not you'll need to find a third party utility, I don't use a third party one so I won't try suggesting one. But you can search through the major download sites like CNET OR Tucows.

Once set up you'll need to monitor & note the idle temps, then with small load then move up to running the programs & games which are crashing you, whatching or logging the temps the whole time. I'm running Intel but I beleive if your temps start reaching 60c to 70C you need better cooling check their web site to be sure.
Athlons run hot & need better cooling as a rule, using a thermal paste is recommended make sure you have good air flow into & out of your case.

Fans also need cleaning from time to time.

The 250 watt PS is only just man enough for the job. I use a 300 watt PS in my system. You should also get the memory checked out, as this could be starting to fail, this happened in my brother's PC last year. Check to see what chipset is on the motherboard. If it is a VIA chipset, there could be a compatability problem between the chipset and the game software. Software patches may be available to cure the problem. I had a similiar problem last year and ended up changing the motherboard for one that had a different chipset; i.e. Aladdin Magic 1.

I would upgrade to a 300 Watt Power supply.

Run a CPU health monitor program and check the CPU temp just after a crash or lockup.
If the CPU temp is over 60C, I would get a better CPU fan.
AMD has a couple of white papers on thermal management.They are worth the time to download and read.

Make sure that the fans on the video card and chipset are working properly.

Make sure all of your drivers and DirectX files are up to date.

Run dxdiag to verify that the DirectX drivers and functions are running porperly.

Did you perform a fresh OS installation when you set up the system?
Or did you transfer over the drive or drive image from your old PC?

If you transfered an older OS installation, you likely have driver file remnants in both the OS folders, and registry keys.

If you are familier with the registry, then perform a search for old device keys, and clear them out.
Otherwise, it is easier to wipe the drive and start over.

Chas

I would seriously consider an upgrade to a 300W power supply but still, these probs are usually symptoms of overheating. After a crash, reboot and go into the cmos...hit "del" key a billion times to get into it ( I am familiar with these mobo's). Inthe cmos, one of the last entries before save and exit cmos is a cpu health checker or something to that effect, go into it and see what the temp is of the processor and inside the case. When you bought the system, did you go with the standard heat sink and fan or did you upgrade?
I have noticed that the standard heat sink and fan combo is not enough to cool the cpu below 60c (150f)..spend a few bucks on a decent fan, it is worth it.
Good luck!

Mike

Yes, the 300Watt or larger supply should be the final fix.

I have seen 300 Watt supplies selling for as low as $20.
I am using Leadman brand supplies that I picked up for $23. What I like about them is that they have an extra cooling fan.

I am surprised that your system is working fine with the Athlon under-clocked.
Normally, when you under-clock an Athlon, all manner of "strange" problems show up.

Chas