ATI Graphics Card R9600XT Problem with Bootup?

Hi There
I recently purchased a Graphics Card off ebay, the Seller told me that graphics card worked fine in his machine , but upon installing it in my machine, it booted up with a set of 6 Vertical Bands with White and Multicoloured pixels.

I havent a clue whats wrong with it, I just am stuck on answers, I have been told it could be a power problem, but dont want to spend any money getting a high watt power unit if I dont need to.

My Current spec is:

Athlon 2800 XP+
512MB PC3200 RAM
20GB Harddrive
300Watt Power Unit
64MB Ati 7000 Series Graphics (working fine)

The problem only arises when I plug in this new card, PS I have tried on to pc's with exactly same result.
Any Clues??