Venue 8 Pro 5830 shuts down after a few minutes

Venue 8 Pro 5830 running Windows 8.1

After a few minutes, the screen goes black and it completely shuts down. When I try turn it back on, almost every time it sends me to BitLocker Recovery, where you have to key in the very long string of numbers. It then seems to work fine for a short time before going through the whole process again. The tablet gets quite hot, so I'm thinking the thing is overheating, but I'm not an expert on these things (that's probably obvious).

I have tried to use the Diagnostic Tools on the Dell website. I have also tried downloading any updated drivers. The problem is that it shuts down again before I can complete anything.

Also, wireless keyboard seems to NOT be working. New batteries installed, but doesn't seem to have helped. I can't move around in the BIOS menu because keyboard is not available. Onscreen keyboard doesn't come up either.

Has anyone else run into this? What do you think is the problem? More importantly, can anyone give me suggestions to fix this!?!

Thanks!