I want to share some tips for working with damaged AutoCAD files. It can be very frustrating if a file becomes corrupt and is no longer in working shape. There are some things you can try to do to recover those files, and some preventative tips as well to prevent them from getting to that state.
First, I want to share a technical solution with some good tips for recovering damaged files that may not even be opening: http://usa.autodesk.com/adsk/servlet/ps/dl/item?siteID=123112&id=2896262&linkID=9240617
Usually, one of those steps will work to bring the file back to a state where it can be opened. Once you get it opened though, you probably want to do some cleanup to try and fix whatever the problems are that caused it to get where it was. Or you may just be working with a file currently that opens, but is slow and sluggish, or just isn't quite acting right and you fear there is corruption setting in. I'll put the steps below that I have had great success with in restoring these types of files back to a clean state.
First, open a blank DWG and run the RECOVER command. You can then browse to the problematic file, and AutoCAD will attempt to repair any errors it finds. Save the file, and then see if everything works as you expect it to. If not, continue on to the steps below:
1) Open the problematic file and make sure all layers are on and thawed.
2) Detach any XREF's.
3) Type in -PURGE at the command line (remember to enter the dash before the command). Type R for RegApps. Delete all RegApps in the file. It is not necessary to do them one by one because sometimes there can be thousands and it would take a very long time.
4) Type AUDIT, and select Y for yes to audit the file of any errors.
5) Type PURGE and purge the file of anything that can be purged.
6) Using the WBLOCK command, block out all the information in the file to create a new drawing. Select the objects by windowing them; do not just type ALL.
7) Open a blank DWG. Do not use any templates. (Set the STARTUP variable to 0, and then open a file if you are unsure if you are using templates)
8) Using the INSERT command, insert the file created in step 6.
9) EXPLODE the newly inserted information so it is not a block any longer.
10) Test to see if the file now works correctly. If it does, you can start to add in the Xref's again one by one. Test the file after each insertion. If the problem returns after inserting an Xref, you'll know that that file needs to be cleaned using these steps as well.
As a final note, I highly recommend running the AUDIT and PURGE commands before each save. This will keep the file clean and greatly reduce the chance of any corruption setting in. You too can have clean files by following these steps!