Rundll32. File

I got a virus a few months ago and it must have messed my Windows up. My problem is I cannot get into my control panel, When I try it tells me that it cannot find the file windows rundll32.exe file. I want to reinstall my windows but I am not real computer literate so dont know how to do it without going into the control panel or if it is possible. PLEASE HELP!!! Im in a mess!!