In this case I would recommend downloading the Intel® Processor Diagnostic Tool that is going to help you to get the real temperature of the CPU.
Could you please sent us the results whenever the diagnostic is done?
When the CPU hit over 90 degrees, did the computer get freeze?
Also, try to reseat the fan one more time and if available can you try with a different fan.
Here is the link where you can find the Intel® Processor Diagnostic Tool Intel® Download Center, third option to install it.
Let me know your findings.
I don't believe the Intel Processor Diagnostic Tool gives temperatures? The Intel Desktop Utilities do though, and they are what's giving the 90 degree plus readings when I run the Diagnostic Tool. This is with the stock cooler installed, and two thorough reapplications of the thermal paste, just to be sure.