i have a ASUS P5B board w/ E6420 running at stock speed 2.13GHz and Arctic Freeze Pro as HSF, i was getting 42-47C idle before i applied Arctic Silver 5 compound, now i'm getting 90C during idle, what's the problem here (is it the MB or the Thermal Paste)?
More abouttemperature problem stock speed
Have you tried cutting down on the amount of thermal paste you've applied? Too much paste will reduce heat conductivity.
Check HS is fitted tightly at all 4 point, sounds like one has come loose.
After you reset reseat the cooler tightly, check your temps from the BIOS before Windows loads up. If it's crazy high then you know your cooler is not seated properly.