Matlab running slow 2013a and 2012b

Hi I have got 2 versions of matlab in my system. Both have been working fine until few days back when both started running very slow. My hard disk has enough memory. There is no virus in the system. Operating system is windows 7. Any clue why is this happening and what can be done? Even addition of two numbers is taking 40-50 secs for results to be displayed.