Do I have a hardware or software problem?

[oggman]

I have learned so much from reading these forums over the years, and I finally have a question of my own.

Not sure if I have a hardware or software problem. How can I tell?

My Computer specs (I know its old but it worked):

Athlon 3200+
K8N Neo F board
XFX 8800GT 512
Lite-On DVD
1 GB Ram (upgraded to 3GB)
Windows XP, SP1 & 2
80 GB IDE drive (upgraded to 1TB SATA)
Antec 500 watt PSU

Here is the situation:

Home built computer has been working fine for my needs until just recently. I play COD2, COH, COHOF, COD4 without any problems.
I got COD World at War, installed it and the game would load, then freeze. I realized my old 80GB IDE drive was nearly full. Thought this could be a problem so I got a new new drive---a 1TB SATA drive. I tinkered in the BIOS got the new SATA drive going then reinstalled XP. I updated all drivers, BIOS updates, etc. Then I read the minimum game requirements and found that COD W@W doesn't run on my old CPU. No problem. I had not installed it yet anyway. I reinstalled COH which used to run just fine. The game loads then freezes and I must restart. Ran all game patches, but no joy.

Here is what I have done so far but nothing has helped:

I took out the new RAM
Took out the old RAM
I got a new inexpensive, $75, (but highly rated 700W) PSU
Unplugged my DVD drive

I have not loaded any other apps yet, so the drive is relatively empty. I'm not really sure what I'm doing in the BIOS, but I have tried to follow the instructions in my mobo manual.

How do I figure out what the source of the problem might be? Any ideas?

How do I know if my mobo is the problem? How about my 8800GT?

It's about time for an upgraded build anyway, but I'd like to see if I can determine the problem before I give in.

Thanks in advance for the help.

Jeff