Try to reset settings in the setting folder in documents/diablo 1 tchernobog. Once i couldn't play multiplayer bcs of that, but maybe in this case it doesn't help...
Let know
Damn... for reset settings i meant to delete at all settings folder, game authomatically will create a new fresh one.
Otherwise i could only suggest you to make a new clean installation with no char in your save (save your chars in another place). If it still doesn't work it's a windows issue.
Very strange... it is very useful to save backup periodically for this reason. I don't think it's possible to fix a bugged stash file, sorry for your loot
Personally i don't keep most valuable items in stash but i give them to a mule char, even bcs if you play keeping them in stash you cannot drop them anymore