Have a problem with installation antivirus program

Hello!
I have a serious problem now after my installation and un-install McAfee Security program. Now I can't install other anti-virus program - I've tried to install Avast, Kaspesrky antivirus - nothing works. Exe. files from these programs just disappear! I cannot also go to the Safe Mode + cannot save any changes after my work on computers. I tried CCleaner (new version) - nothing works again. When I try to make sfc /scannow - PC does not recognizes my CD (I have original genuine CD). I cannot open Internet Explorer (got message "Windows cannot find "null".....). Now I use Mozzilla Firefox. I tried to repair my Windows - nothing - everything the same!
I use Windows XP SP2.
I'm not a BIG programmer....So...Please, help!

Thanks, ahead.