PC freezes randomly, could it be the GPU?

[nuclearvw]

Hello,

I recently built my first PC with:

Western Digital Caviar Blue WD5000AAKX 500GB
G.SKILL Ripjaws Series 4GB (2 x 2GB)
AMD Phenom II X4 965 Black Edition Deneb 3.4GHz
Rosewill RD400-2-DB 400W ATX V2.2 Power Supply
ASUS M5A88-M Motherboard

I then purchased a Sapphire Radeon HD 5450 graphics card.

Since installing it, my PC will randomly freeze, every time I start it.

I have since re-installed Win 7 64 bit, and removed the hd5450 (Mobo has integrated hd 4250) but it still will freeze.

I have also installed the drivers given with the Mobo.

The freezing starts by having the windows being non-responsive and then the mouse will stop moving. Ctrl+Alt+Del doesn't work.

What can I do?

 

[nuclearvw]

Update:

I successfully installed the drivers for the sapphire as well as the card itself, it ran for about 2 hours and then it crashed again...