Unable to start MS Excel 2013 after the upgrade

I was using Microsoft Office 2010 and it was working perfectly. Recently I have upgraded it to Microsoft Office 2013. The upgrade went perfectly fine. But from then I am unable to start MS Excel. It is opening the window and then getting stuck. Nothing seems to be progressing at all. I have looked into the task manager and it is consuming lots of resources/CPU. I have stopped and restarted MS Excel several times, but no use. I have restarted the system also but still no luck. What could be the problem here? Can somebody help me out here.
