Do you have any other games or resource intensive applications, and do they cause any problems?
The rebooting may be a power supply problem if other programs do the same thing. Crashes and lockups can also be due to a heat problem, but I don't know about reboots.
Did you update your chipset drivers along with the rest of the driver updates?
If it is a memory leak, the topic
Awful Slowdown contains some information on RAM programs and settings.
There are a couple memory testing programs you can try;
Memtest86 and
MS Windows Memory Diagnostic.
