Cad
 

I have insatlled AutoCAD on my Laptop. But it doesn't open it's own file (DWG extensuion).
Error message "Internal Error".

The file is on my desktop. What do I need to do?

If the CAD file you are trying to open was saved from a newer version of AutoCAD than the version installed on your computer that might be the problem.

Try running a repair on the program. Or a reinstall. If it was saved in a newer version, it would tell you something along the line of "The drawing file cannot be opened because it was created with a more recent version of AutoCAD".

It can be error in third-party ObjectARX application which open AutoCAD object ForRead but attempt to modify it. You can try uninstall or disable it and check pure AutoCAD.
For better suggestion on issues related with AutoCAD have a look to here OnlineFile.Repair.AutoCAD