Black Screen

[Metaknight]

After the cake thing, whenever I enter a game, the scenery becomes black. I see worms in inverted colors but the rest is black.
Operating System Windows XP
DirectX Version DirectX
CPU Model/Name Intel Pentium 4 Processor with MMX(TM) Technology
CPU Speed 2.4GHz
# of Processors 1
Total Physical Memory 512MB
% Memory Used 65%
Resolution 1024 x 768
Color Depth 32-Bit
Free Disk Space C:\ 8.90GB
Free Disk Space D:\ 7.94GB
Free Disk Space E:\ 271.36MB
Free Disk Space F:\ 837.61MB
Free Disk Space G:\ 287.94MB
Max Swap File Size 1.22GB
Available Swap File 877.44MB
TCP/IP Protocol Installed
IPX/SPX Protocl Installed

It worked fine one week ago, when suddenly...
Wats the problem? Resolution, graphics card?
Games like Spore, Neverwinter Nights 2, The Battle for Middle Earth, even Worms 4 work.
Can you figgure the problem out?