Also, many dell pc's have a recovery mode accesible from the boot screens. Often its f10, but check to be sure. This recov process usually doesnt require cd's. Did you receive product cd's with your dell, or was it just an install of windows and no cd's? If that the case, you will have to look at possibly buying a copy (if there's no recovery progs), or maybe look at uninstalling stuff, cleaning up the registry.
I am sure you already tried this but how about the easy stuff, like defraging your drive(s), double checking that you have at least a gig free on your HD?