Game Loading Problem

[Blakcm2]

I'm not sure whether this is my hardware or my software, but I have a problem loading a game that I play over the internet.

Specs:
Western Digital Special Edition 80GB 7200RPM IDE Hard Drive
Corsair Value Select Dual Channel Kit 184 Pin 1G DDR PC-3200
ABIT "IS7-E" I865PE Chipset Motherboard For Intel Scoket 478 CPU
Intel Pentium 4 2.4GHz 800MHz FSB, 512K Cache, Hyper Threading Technology
350 Watt Powery Supply with only 3 80mm fans running
NVIDIA GeForce 5600
OS is Microsoft Windows XP Pro

I have DirectX 9.0c. The game is Battlefield 1942. I have both the 1.6 and 1.61 patches. I have both Windows service packs. It is the original game, no modifications. I've already downloaded the mobo drivers, integrated sound drivers, and video card drivers.

Now, to the actual problem; I go through everything okay. I select the server. Loading the map up until it finishes is fine. When the loading map is fully finished and just about ready to go to the Server Welcome screen to play, my computer totally restarts just as if I would go to Start:Shut Down:Restart. The game doesn't crash to desktop or anything. It completely restarts.

So far, my guesses for the problem are either the power supply, maybe? Or the memory; is it being recognized but not working? Any other ideas? I'm new to the site, recommended by somebody, and I hope to resolve this soon. Thanks.