Memory problems

I'm in need of serious help.

Two weeks ago I was hit by a virus which locked me out of my PC.I decided to wipe my harddrive and start again however this is where the problems really began.Everytime I tried to reinstall XP I was getting a lot of errors about missing files and not being able to copy files.This was resolved by removing one of my 1gb ram sticks.My pc now runs fine except when I try to use both of my ram sticks.Everything goes mental, crashes, blue screens, errors of all kinds, the lot.

I have used both memory separately so I know there is nothing wrong with the ram.My Pc is quite new and this is the first time I've had any problems with it.

This is my spec.

CPU:INTEL® Pentium® DualCore E2180 (2.00GHz)800MHz FSB/1MB L2 Cache
RAM:2GB CORSAIR DDR2 667MHz(2x1GB)
MOTHERBOARD:ASUS® P5VD2-VM
OS:Win XP Pro
HDD:160GB SERIAL ATA II HARD DRIVE WITH 8MB CACHE (7200rpm)
GRAPHICS CARD:512MB GEFORCE 8600GT PCI Express
SOUND CARD:SB X-FI

Any help would be greatly appreciated.