I would guess that Windows is pointing to the wrong place - especially if you moved BIAB. Your BIAB files should show up in the folder with the BIAB icon. If not, open a folder and choose Tools|Folder Options... and select File Types. Scroll down the files until you find a BIAB type such as MGU. Select that type and press the Advanced... button. There you should see the Open and Play association. Hit the Edit button and that should show you where Windows is pointing to. If it is not correct, fix that and your associations should be OK.

R