Below please find specifications for my newly build PC:-

Processor: AMD FX4170 Black Edition w (stock heatsink)
ATX MOBO: ASUS M5A99X EVO, AMD Chipset 990X/SB950, UEFI BIOS
AM3+ socket
Memory: Corsair Vengence 8GB DDR3 1600
GRAPHICS: NVIDIA GTX560 TI, 1GB DDR5
PSU: NZXT 750W HALE82 Semi-Modular
CASE: NZXT Phantom
Operating System: Windows 7 64 Home Premium

I installed the following and left it idle and suprisingly I watched the CPU temp rising from 29 degres to 49 degrees.
Mobo drivers, software and utilities from mobo dvd.

After observing that, I rebooted it into BIOS and set the boot sequence as follows:- USB, DVDROM then HDD. Then I shut down unit once again and reboot to desktop and installed "System Monitor" and "Core Temp" . Core temps read between 80'C to 83'C. I shut down unit immediately. I felt heatsink and it was barely warm, around room temp. I removed heatsink, inspected, reseated and reboot again with approximately the same temp readings. Which readings can I trust, if any one of them?

I am now scared of leaving it idle. Let me hear your suggestions.