In the new database
Select the External Data option (tab)
Select Access Database
Browse to your old database
Select one table and try and import this
if this works then do the same again but on another table
Keep doing this until you find something that will not import
EDIT
Just had a thought - in wondows explorer
see what size the DB is as it may have bloated whilst you were working on it ??
You could also see if any of the tips here will help
http://support.microsoft.com/kb/310937
You could always try and decomplie the old DB from the start/run menu but this way may lead to loseing some of the data. Best bet would always be to try and import the tables/forms/etc and see where it stops. Then bring everything (to the new DB) that
is OK - at least then you'll have a backup (of most of the old DB) if the decomplie messes up everything.