Windows cannot find files,

Hi there I am running Windows XP home edition SP1 been having problems with
DOS mode for a while,cant stop Dos mode,get error messages that Windows
cannot find files,or applications,which I need to run programs etc.I know the
files still exist but cant seem to get windows to find them,have modified
path in System environment value to ;c:\appdir still no change,have created a
..udl file still no change.The files are mainly dll & exe which cant be
found,I had installed SP2 but to no change in situation,so have uninstalled
till I can resolve the problem.I cant find the Backup file,also have an error
of This program cannot run in Dos mode,needing some help desperately,thanks
for any imput,I do not want any programs to run in DOS,please,please,help me.
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J.L.Gazzard