You are unable to open a CAD drawing and need to recover the file.
A number of issues can prevent DWG files from opening. The file may be too large to open, which causes CAD to crash, or the drawing might be corrupt.
You can use the RECOVER command to attempt to recover the drawing. Type Recover in the Command line, then press Enter.
The Select File dialog box will open. Navigate to your file, select it, and click Open.
AutoCAD will now attempt to recover and open your file.
If AutoCAD is able to open the file, we strongly recommend cleaning your drawing. This process will rid the file of all corrupting elements and, if all goes well, make it easier to open next time.
You may also need to remove any unnecessary Xrefs from your drawing. Some Xrefs are overly large and cause drawings to collapse. Others have corruption in them and require cleaning. (That's why we recommend that you detach and clean all Xrefs – or clean them before you attach them.)