First, make a backup of your file.
Then, from the menu "Tools", "Database Utilities", try the option "Compact
and Repair Database". You can also create a shortcut and add the option
"/decompile" : this will strips the compilated elements in your database
before opening it and will help a lot with the option "Compact and Repair
Database".
You may also try to create a new database and import all of your elements
from the old database file. If you have Access 2002 or 2003, you can also
try to convert the database to the Access 2002 format then back to the 2000
format (if you want to, of course).
Finally, make a chearch on Google with the words "recovery access database",
you will find services and tools for repairing Access mdb files: maybe some
of them are also able to recover ADP files.
S. L.