Hello, praying someone can help us

Set Up is

Motherboard : Biostar K8NHA Grand V1.2
Graphics Sparkle GForce 6600 256mb
Athlon Sempron 3000
Hard Drive Maxtor Diamond 200G
Memory 1 Gb DDR 400
PSU 500MW

Just bought new Harddrive (the 200gb above) and suddenly my Graphics card has problems (white lines across screen etc when playing games).

Anyone know why?

worked perfectly with a 120G hard drive