I suppose you've tried the obvious, like rebooting the computer and trying again, but here's some other things to try:
Are you trying to open it by clicking on the .accdb (or other such) file, or by opening Access first? If the former, what happens when you do the same to one of the earlier backup copies you hopefully have? Or to another database, if you have one?
Try opening Access itself first, then navigate to the database and try one of the Open options like Read-only, or Exclusive (dropdown arrow on the Open button at the bottom of the window). Note exactly what happens when.
Try opening Access then opening a new database. Does this work?
Any of these things might possibly give a starting point for where to look.