Speedfan is a great program that will display your computers cpu, hard disk & gpu temperature. This is handy if you want to see how hot your computer is.
After time your PC will gather dust inside and your cpu may get hotter over time due to dust build up in the cpu heatsink. This will mean the heatsink is struggling to do its job of cooling the cpu as dust is getting in the way. Search on Youtube how to clean your cpu fan for more info.