Live view in Nikon DSLRs is intended to stop after 30 seconds if you're not actively using the camera. This is very useful, as live view is very hard on the battery, and it would completely draw it for no reason if left unattended.
Also this is not a problem in actual use, as countdown should stop and reset to 30s whenever you do something (e.g. correcting exposure, taking a photo, changing some settings). If you start video recording (OK button) it should go on as expected until it hits its time limit.
You may have a problem with video recording not working, in which case your only option would be to have your camera replaced or serviced. But your question (and comments) seem to imply you did't have problems with video recording stopping before it was time or not even starting, as you just mentioned the 30s LV limit.
The part of the manual you're quoting in the comments is about how shooting of video, or stills for that matter, is supposed to stop if the camera is overheating. This is standard in most cameras, as far as I know, but it's very unlikely to happen unless you're doing very long exposures (I'm talking hours).
Some notes: the OP never mentions trying to start video with no results, or recording interruptions. So inferences are being made with no premises to support them. I took the trouble to have a look at the manual even if I already knew roughly how the camera worked, so I found out the 30s countdown is dealt with in the "live view" section, and the part about recording interruption in case of overheating is in a box of its own.
On top of that, putting the camera in the freezer is the worst thing one could do, exposing it to condensation problems and temperatures it wasn't designed to handle.