New RAM upgrade gives BSOD.

Hi, first off i apologise if this is in the incorrect location.

I own a Dell E520, warranty expired and the only upgrade made so far is a new 8600GT Graphics Card.

I decided to upgrade from 1GB to 3GB of RAM. So i looked in the online manuals for my computer, these of which told me that i require DDR2 Memory, Non-ECC, unbuffered. So, i bought two 1GB sticks of Corsair RAM from Amazon. Of course, these were Non-ECC, DDR2 and Unbuffered.

My problem is that after starting a computer, it can run for 3days without BSOD, however sometimes only 15mins before i get the BSOD. I have only got this since the upgrade. I have, like the manual told me set up the RAM like this.

DIM 1 -512mb

DIM2 -1gb

DIM3 - 512mb

DIM4 -1gb

I have also tried other varieties of putting them in but still no luck, could anybody please help me? I don't understand why this is happening if i have bought the correct RAM.

Thanks.

P.S. I have also ran virus scans ETC. but my computer appears to be clean. Just a thought, could i be in need of a new PSU to deal with this power and the 8600gt? I have hopes to also install a new HDD in the future...