windows xp rejects installation cd’s

my windows xp operating system suddenly started rejecting installation cd’s such as aol 7.0, 6.0 or any other cd to install programs. the message “config.nt the system file is not suitable for running msdos and microsoft windows applications chose close to terminate application, the choice boxes are close and ignore, select either one and the program terminates. I have dual boot with win2000prof and it works just fine so proplem is in xp. Microsoft has suggested 1. reinstall config.nt and autoexec.nt, reinstall windows xp, manually construct config and autoexec.nt, I tried all this with no help. can anyone give a clue on fixing this problem? thnaks