Computer Freezes up... (HELP!!!)

When I have a browser open (I use Firefox).  After a few minutes, my computer freezes up, i can click on anything, etc. I open task manager and there are two iterations of the same file, cssvchst.exe, running at the same time. (in fact, now there are several duplicate processes running simultaneously).   I have to end process on one of them to get my computer screen back.  It works for a while and then freezes again...I have to perform the same procedure over and over and over.  What is this file and how do I get rid of it.  My computer has been acting this way for a couple of months now. 

 

Thanks!

Mindy