Command & Conquer Zero hour different on 2 PCs

Hi, I have two systems, identical except for the amount of ram, that both have C&C TFD's Generals and Zero hour installed, from the same DVD.

System 1: I7-920 6gb DDR3 1600mhz, WD 500GB Sata HDD, ex58-ud3r Mobo, Win7 x64 Ultimate, gigabyte GTX260 graphics.
System 2: I7-920 4gb DDR3 1600mhz, WD 500GB Sata HDD, ex58-ud3r Mobo, Win7 x64 ultimate, gigabyte GTX260 graphics.

Both have all the latest M$ patches, and are running nvidia 195.62 drivers, same BIOS revision on both Mobo and graphics. Both are running DX 11. Both have the same applications installed.

I spent hours last night trying to find differences in the systems configurations, applications and so on, but nothing was found. We are even running the same versions of applications.

Yet, When attempting to run Zero hour on System 1 it crashes saying "You need Directx 8.1 or higher" whereas on System 2 it runs fine.

I'm tearing my hair out... can anyone help?

thanks
Tanya

This is the only game that is on several machines. There are other games on each of the other machines that work fine, but I only have this one game on my computer.

I did download the latest DX, that did not solve the problem. I even tried installing DX9.0c most recent dist, and that didn't help eaither.

I recently gave up on this problem and dropped the game. However, for other reasons I reinstalled my PC with a faster hard drive and enabled AHCI. I then reinstalled the game, and it worked fine.

Buying a hard disk and enabling AHCI is hardly a solution to this prooblem, and I guess I will never know what the cause was, but at least it now works.

thanks for your help.