Please write down ALL your system specs here.
See if you PSU is enough here:
http://www.jscustompcs.com/power_supply/
This error leads to the same of our BSOD's: hardware or drivers. Since you already replaced most of the hardware, I think it's either incompatibility(from memory) or some driver. Try a clean install with minimal configuration, just one stick of ram(see in your mobo's manual if there's a preferred slot when you use 1 module), one HD(cable select) and the video card. Maybe cdrom too so you can install things, but don't install anything unless it's absolutely necessary. Then update to XP SP1, install most updated chipset drivers and vidcard drivers. Run Prime95 for a day and see what happens... if it's good, create a system restore point and install one more hardware. Go on this way. If it turns bad, restore the system to the previous state and now you know what's causing you trouble.
Before all that, run memtest86(latest version, bootable CD) if you hadn't yet.
I had a really weirdo problem some years ago, caused by pure stupidity hehehe. The cooler I was using was VERY heavy, and it was stressing the mobo, so I put some other screw holders(this is not the correct name, but was the best I could think of
😛) to support it better. Problem was that they were creating shorts!! Just putting some tape solved the problem, but I've gone through A LOT to find out that this was the cause
😛
So think of these things too, maybe you didn't install something right. Remember Murphy's Law
😛