Hi. I have a new Gigabyte GA-8N-SLI mobo. I also installed 4GB OCZ DDR800 SLI ready. Since installing these my computer has been freezing. Like no keyboard access, no mouse movement, nothing. I checked out my northbridge chipset (nForce4 Intel edition)and it usually runs at 60°C (not under load). This seemed to be very hot to me. Could this be causing my instability?
Yes, 60C is too hot for a chipset, and when a chipset overheats they're the exact symptoms. I'd recommend replacing the chipset cooler with a Thermalright HR-05, which you should attach using Arctic Silver V.
Unlikely unless they're insanely wrong. Changing RAM timings gives performance benefits, but them being wrong won't render your PC unusable.