I have encountered a problem trying to backup a dos program open in Windows. (This has worked perfectly previously).  I did reinstall the dos program without resolving the problem.  I get an error message "CS:128f IP:0dd0 OP:fe 20 b5 05 eb".  What would this imply?  And can I try and restore Windows XP? (When I tried and used the disc that came with the computer I'm told a newer version was installed and that the prior version, on the disc, is therefore not appropriate.)