Firstly, close Access.
Open the folder where the mdb file is stored.
Delete any LDB file in that folder.
The LDB contains locking information for the MDB.
If Access crashes, the LDB may contain spurious info.
Then try importing everything into a new database.
Follow the steps for the first symptom in this article:
Recovering from corruption
at:
http://allenbrowne.com/ser-47.html