If the drawing file (DWG) will not open at all:
Your drawing may show the message "Drawing file is not valid," display a message about errors being found, hang or crash during the open process, or simply may not appear in AutoCAD after you have selected to open it (i.e., you open it but all you ever see is the default "Drawing1.dwg" or another file that you currently have open).
Use the following article if you receive the "Drawing file is not valid" error when opening the DWG: Error: "Drawing file is not valid" when opening a file in AutoCAD.
You might have leftover .dwl or dwl2 files in the folder directory. These are two hidden files that have the same name as the .dwg file but with the extensions .dwl and .dwl2. In the Windows Control Panel, go to Folder Options. On the View tab, turn on the option to show hidden files. You can then go back to the folder directory and delete the .dwl and .dwl2 files if they are found alongside your DWG file. Attempt to open the DWG again.
