Cannot Open C: DIR/DIR/yourtext.txt file
Make sure a disk is in the drive you specified
Have you tried running ScanDisk? If a portion of the harddrive near the beginning of this file is corrupted in some way then the file won't open. Also, is it just this file or all Notepad files. If it is all notepad files then I would try opening it with another piece of software like wordpad or notepad ++. If you give a few more details we may be able to give more suggestions.
Philip
MSCE, MCSA, CCNA