I have had this problem in the past. When the database exceeds it's maximum size of 1Gig Access falls over badly as the system tables get corrupted. Your database is 500Mb and probably expands rapidly when you are using it (without you realising that it has expanded).
You can try the following:
Create a new database and copy all the objects except the tables to the new database. Try to link to the corrupted database and link back the tables.
If this works you could try and copy the linked tables to a new table in the new database (very laborious if you have lots of tables).
You might find that it is only one or two tables that have been corrupted. you might have to recreate these tables yourself from a back-up