That's tricky! Files and environment looks fine. That leaves 2 solutions:
1. bad motherboard
2. bad video card

When starting Reflex, it interfaces with the DirectX 8.1 3D engine. This piece of software interacts with the video card and immediately lays hands on the video ram. If you do a google search with "7VRX" and "motherboard" you will find a lot of issues referring to the AGP bus of this particular gigabyte motherboard. Please try installing the latest BIOS from www.giga-byte.com.

On the other hand, it could be the video card. A simple broken memory chip on the video card could spoil the computer. That won't happen in a regular XP/office environment but it could happen with complex 3D applications. Please download 3DMark from http://www.futuremark.com/ and run the prog. You video card should crash as well.

3rd possibility but rather faint: your power supply! The 9800 needs about 30 VA during regular opperation but sucks up to 150 VA in heavy 3D mode. If you only have a 200 VA power supply PLUS a few hard disks PLUS a few CD's/DVD's/non-AC USB printers or scanners ... your powersupply could go dead after starting the Reflex.