For the OVerclocking error, access the BIOS upon startup by hitting the 'Delete' key. Usually it's that button that gets into BIOS setup utility. Once in there, look for an option to change to default settings or something similar and save it. Then it will restart. It basically go back to stock.
As for the program, you need to download the Everest Home Edition first onto your hard drive. Once finished, just open up the folder and there should be a Everest.exe icon for you to double click on. A window will open and click on Motherboard/Sensor. That will give you your CPU and GPU temperatures.
You can also view your CPU temp. from your BIOS too.