Computer Keeps Freezing

I've had this exact set up of hardware for a little over 6 months with no problems, but about two weeks ago my old hard drive failed. I picked up a new hard drive, installed windows, updated windows, and then installed all my drivers. Nothing new, I kept all my files on a seperate HD and formatted windows every couple months.

But something is really screwed up now, and I don't think it has to do with my new hard drive. I cannot last more than 5 minutes in a resource-intensive game like Rome: Total War, Battlefield 2, or World of Warcraft. Sometimes, but far less frequently, I lock up while just browsing the internet and chatting on AIM. It seems it only does this while I'm actively doing something; I've left my computer on overnight several times, and not once has it been frozen when I returned.

When I freeze, the picture becomes frozen and the last ~0.1 seconds of sound (if there was sound playing) repeats non-stop.

The monitor doesn't turn off, so I don't think it's a problem with my video card, and because it also freezes when there's no sound, I don't think it's related to my sound card. Neither of those assumptions are very solid, but my guess would be that it's related to my RAM. However, when I used this memory testing program: http://hcidesign.com/memtest/ I didn't receive any errors.

I know this is very broad, but I'm all out of idea's. I've formatted windows twice, tried different video drivers, disabled my sound card, reset my BIOS to default and tested each change of the settings seperately and in combination, and used that memory testing program.

What else should I try to narrow this problem down?

Windows XP Professional
MSI KT4 Ultra VIA chipset
Athlon XP 3200+ 333fsb
Radeon 9700PRO 128mb
768MB DDR (512MB stick of PC2700, 256MB stick of PC3200)
Soundblaster Live 5.1

My first thought is PSU.
Second is blown caps.
Check PSU with Digital MM. or
Do you have another PSU to test with?
How about Sound blaster drivers, do you have the latest?
Just a few things to check off the top "O" my head.
GL,
Killa
Oh yes, to the forums. Once everyone gets a look at this I'm sure we can figure out your problem.

Just like the guy above me said, try switching out the Power Source and look for any burnt capacitors. I'd also suggest using one stick of ram. On occasion incompatibilities between the individual sticks occur due to brand or speed ratings.

Finally, use a reputable program like motherboard monitor 5 to check out the temperatures of your CPU and the voltage rails on your PSU. If the 5v rating falls below 4.98 at any time then it's time to get a new power source; likewise a CPU temp of over 60 degrees celcius (for your particular processor) is a very bad thing. A good number for the 12v rating would be anywhere above 12 volts. Anything below 11.8 is very bad.

It looks like my 5v rating is well below what you stated. Is this most likely the source of my problems?

Anyway, I really never thought of the PSU as a critical component and I know practically nothing about them. What should I look for when I go shopping for one?

Start by reading this.
Dose your MB come with software monitoring? You really can't trust MBM or any software to give you real voltage readings. That's why I linked you to the DMM page.

Sorry, I don't see a link to a DMM page.

I just checked my voltage ratings in my BIOS and they are different. For the most part, the 5V rating stayed at 5.003v. Sometimes it would drop down to 4.975v.

There was another thing called +5V SB that was rated at 4.921v.

OOppps This link will help you test your PSU with a Digital Multi Meter. This will give you actual readings.