I built this new system with i7-920 on an ASUS P6T with Thermaltake SpinQ Heatsink. When I boot my system up, my cpu reaches 80 celcius on the bios???? I did put very thin layer of thermal grease and plugged the heatsink into CPU fan plug and ignored 4th pin. Wow, 80c after like 20 seconds, how is that possible?
Yes that is possible - but clearly indicates either the fan / HSF is not very good, but more likely it is not seated correctly. I often attach HSF's with the mobo outside the case to make sure of a good fit.
Remove the HSF - clean off the TIM and then reapply a small amount (AS5 or MX2) and re-seat the HSF.
Everyone at some point has had similar issues - especially with the more recent Intel push pin crap design.