Cpu temp freezes on running everest

Hello,
its a very interesting but puzzling issue arising out of my pc...my cpu idles at 18 C & hits 42 C under prime95 stress tests. Recently i've installed Everest Home edition on my pc. but when i run the software & click on the 'sensor' tab to monitor temps ,vcore etc, the cpu temp freezes at once. right from then even if i run 3D games or prm95 for hours the temp remains fixed till i shut down the pc. as temp is fixed, no change in rpm of cpu fan occures...I've touched the case by hands to see if there is any heat generating due to the games/p95. bt no, there is no change of the case temp even. please explain whats happening in that case..
thanks