1) run MEMTEST www.memtest.org (full pass)
2) 10GB of DDR3 memory is an odd number. (is that 2x3GB, and 2x2GB??) Thus you're mixing memory though if MEMTEST passes there's a good chance there's no stability issue.
3) SINGLE PLAYER works fine?
Hmmm...
If it's only multiplayer then it may be NETWORK related. Not quite sure how to help at this point.