objects disappearing in AutoCAD 2013

[gb.andris677909]

I just started learning AutoCAD 2013, tried to model a tank and after a day of work the turret disappeared with all its details, and it's only visible when I rotate the whole model, without being able to interact with the non visible piece in any way. Is there any way I can recover the missing object, or at least permanently delete it and remake it afterwards?
comparison picture.jpg Here is the .dwg that I worked on: Panther ausf g.dwg

[jaberwok]

I just started learning AutoCAD 2013, tried to model a tank and after a day of work the turret disappeared with all its details, and it's only visible when I rotate the whole model, without being able to interact with the non visible piece in any way. Is there any way I can recover the missing object, or at least permanently delete it and remake it afterwards?
comparison picture.jpg Here is the .dwg that I worked on: Panther ausf g.dwg

Hi, welcome to AUGI.
The bits in your lower window are all that is in the file.
Manually deleting the visible parts leaves only one (theoretical) object with zero volume.
Sorry.