Thanks, Tom -- any clues on how to get my layer manager box back?

I am trying to export a very large file to a dwg or dxf file. The starting file (created by another coworker who is out on disability) is over 85 MB. I have tried purging it to no avail. When I go to export (just need 2D model), it just sits there and finally says "not responding."

Another issue is that when I push the layer manager icon, I do not get a layer manager window.

Any assistance on these issues would be very appreciated. I've started going through the tutorials, etc., but need to solve this issue quickly in order to meet a deadline.

Thank you!