Right click of mouse is not working

The right click of my mouse is not working. My friend is the last one to use my personal computer at home. I did not take it as a joke when he told me that he'll play along with my PC and I have to resolve the issue myself. I guess I am challenged so I tried to check the mouse settings, however, all are in place.
Bad timing, I was so lazy enough to search this on the internet. Rather, I just want to wait for someone who will provide me the answer and then I'll try if this will resolve my issue. I have asked another friend and gave me an idea that it can be in the registry edit, but I do not want to touch it unless I was sure on what to do. Kindly help.
