MS Office Word 2001 - losing file format when I save.

I am confounded by Word in MS Office 2001.
Every day I am finding that stuff has lost all its formatting and it is a nuisance putting it all back.
I have uninstalled the software and reinstalled it but that makes no difference.
I have autorecover on.
I have recently installed a Wacom digital tablet (conflict?)
I am not sure whether this is linked to freezes, which have happened form time to time.
Sometimes the formatting magically reappears but I am not sure what I have done to make that happen.
Most often I open a document, like the one above and when I try to save it I get a dialogue box up which says

"This doc will be saved in a Word format. Do you want to continue?"
Hitting "No" obviously does nothing, and "Yes" just saves it still without its formatting.

I find I can keep the settings by saving direct to my zip disk, which sounds ominous.

Any help?