Desktop problems after WinXP Reinstallation

Thanks to my wonderful Dell technician, in diagnosing a bad memory card, he managed to corrupt my Win XP so badly that after 4 hours on the phone the only thing he could offer was to backup everything that I could on my hard drive, reinstall WIN XP and start over. He had erased my start icon and I could not get to any programs unless I entered through the directory. I called back and got another technician who simply stated that all I had to do was to reinstall my original WINXP over the old one and everything would be all right. It worked up to a point. I now have at least two BIG problems that I cannot figure out what to do about. 1) After I download or copy any file to my desktop, when I move or copy it somewhere else, it is corrupted and it will not work and it will not even let me access or even delete that file . When I go to access the file, I get a message that says the file is in use or is copy protected. I have done this on numerous files and not one has worked after it is moved, copied, etc. from the desktop 2) No matter what I do no screen saver will work! I have no idea what the problem is because everything else pretty much works. Any help would be greatly appreciated.