Windows error: windows cannot find rundll32.exe

I need help with my Deminsion 3000, everytime I try to open the control panel I get this message: windows cannot find c/windows/system32/rundll32.exe.

when I am on a website i cannot enter information into any of the boxes, for instance if I was on the computer i would not be able to enter the information into this box. Can someone tell me what to do to stop this error?

I've tried to reinstall the windows cd but that didn't work.

thanks,

Caroline