It may be a dying fan. Look for strange noises or buzzes cominf from every fans. Also try to make them spin with your fingers: if it stops spinning in a few seconds then you need to change those buggy fans.
Someone needs to warn people that speed fan is not a reason to start going crazy as it gives bad readings.
I downloaded it on my new pc it said my cpu was -68 and after my pc came back up after a 2 hour sleep it said 120.
I down loaded Core Temp and everything has been fine as it seem to read the correct Temp. Perhaps Speedfan does not read the i5 and i7 CPUs correctly.