This error would occur when VC cant detect more than 12MB of usable graphics memory (NOT system memory).

This would happen due to bad/no graphics drivers installed. It may also happen if all the graphics memory is being used. Since it worked before i would say his system has either broken itself, or hes uninstalled the drivers without knowing what hes doing. Or hes running another game in the background on a low end graphics card with very little vram.

Kingston: Can you provide us a screenshot of the display tab in dxdiag (If your running XP, go to start -> run then type dxdiag In vista or 7, type it in the start menus search thingy)

This will say the graphics card, driver information and detected graphics memory, aswell as any problems detected.

What's your graphics card?

Aren't they mobo's?

1. Many times on forum.
2. Reboot system.
3. Have you installed last time some new graphic drivers etc? <doubt>