If a file can be opened but still shows signs of corruption, take the following steps or see and learn next topics about AutoCAD file corruptions, moreover the last solution can help you if your file was severely damaged by unknown reason - https://dwg.recoverytoolbox.com/
Recovery Toolbox for DWG
Use the auto save files to recover your work:
1. Go to Tools --> Options.
2. Inside Options go to the “Files” Tab (far left).
3. Inside the files tab go to: “Automatic Save File Location” and see where the autosave files are stored. (Mine where stored at C:\Documents and Settings\USERNAME\Local Settings\Temp)
4. Then access that folder and try to find a file with the same file name but different extension. (The auto save files should have a either a .BAK or a .SV$ extension) (if you can’t see the folder, you need to go to Tools --> folder Options --> View --> and Make sure "show hidden files and folders" is SELECTED) .
5. Check the "date modified" of those files, if the date and time makes sense according to when you had the last file crashes, there is a good chance that those files contain the information you need, so there is no need to redraw everything.
6. Change the file extension of the file you think it might be the good one from .bak or .sv$ to .dwg (to be able to change the file extension you need to be able to see it. To do that, on any folder go to Tools --> Folder Options --> View --> and make sure that "Hide extensions for known file types" is UNCHECKED)
If your auto-save feature is disabled, you can enable it in AutoCAD by going to Tools --> Options --> "Open and Save" Tab --> and there make sure that the "Automatic save" on the lower left corner is active and preferably set to every 10 minutes or less. To easily change the time of the auto save feature, use the SAVETIME system variable