First off, my technowizard skills are limited.

I've been experiencing sudden shutdowns these past months. First thought the problem was with my graphic cards running too hot. Then I tried running with just one but still the crashes persist.
I'm pretty sure its not my RAM blocks overheating (have a corsair fan ontop of the 2 I have).
My temperature readings now point me towards the NB and SB. I run PC Probe II V1.04.76. All my temperatures look more than fine, with CPU on a constant 15 degrees (watercooled) and NB 34 and SB 34-38ish. Except now when I keep PCprobe running, SB suddenly jumps from 34 to 95 and then back, leading me to think the sensor or the program is faulty and I have a very hot SB.
Should I be worried the readings aren't accurate, even faulty? From what I've read NB and SB temperatures should be kept below 90 degrees. And now I've just read pcprobe isn't the most trustworthy when it comes to reading temperatures. Any suggestions?

Specs are as follows:
OS: Windows 7 Home Premium
Motherboard: ASUS Maximus Extreme
Graphics card: Nvidia GeForce 8800 GTX (x2, only running with one now)
RAM: 2xKingston 2MB blocks