Has this camera (D800) been recalled for any problems?

Is it possibly a menu setting which has inadvertently been changed?
There is also another response on this forum dealing with batteries which have been recalled - has this any relevance in your situation ?

Believe it's China but don't quote me. Here is an excellent article on the D600:
http://kenrockwell.com/nikon/d600-d800-d4-are-the-same-camera.htm

There are many solutions, here is an example:
http://www.pocketwizard.com/products/cable_accessory/flash_sync_cables/

There are differences in technical specification of those 2 cameras.
And the resulting images too have differences.
see the following site for comparison:
http://www.bhphotovideo.com/explora/photography/hands-reviews/discerning-differences-between-nikon-d800-and-d800e

Of course the D800 is full frame and the DX 18-135 is a DX. The only thing the D800 needs to do is switch to DX mode. The Nikon FF camera's can work with DX lenses. (if the lens has a chip) You still have a nice 15 Mp picture on the D800. But if something was wrong with the lens, you should have an error on the display.
Please to check the lens, switch to live view. You should see something. If not, really something can be wrong.
Carful go to taking a picture step by step. Be sure the lens is correctly put on the body. But before you put it on, look is all contacts are clean shiny and there are no dents.

the problem is not for your battery but the problem is with your hardware

replace either your cold cathode screen lamp or, your inverter board in your display

sounds like a memory allocation issue..check that first

This may be SpeedStep slowing the processor to save battery life. It speeds up when it is needed.