One of the easiest ways to open your drawing is by dragging your file to your CAD title bar.
If you can’t drag n drop to open, one possible reason is that the SDI system variable is accidentally set to 1, just make it to 0 and see if the problem is solved.
SDI, or single-document mode, only allows only one drawing to open at a time. The default value is 0, which allows more than one drawing to be opened at a time. When set to 1, SDI is enabled and only one drawing can be opened at a time.
We don’t normally change this value, but some software for further development might change this system variable.
PS: Another reason for failing to drag n drop to open the file is there is running function already in your CAD, remember to turn it off.