I have a 50" DLP Samsung that keeps turning off by itself

There can be several causes for this, few of which you can do anything about. However, a few things to try:

1) Replace the batteries on your remote control.
2) Try resetting the logic functions on your tv by unplugging it for a minute, then plugging it back in.
3) Try covering up the infra-red receptor on the front of your TV to see if you're getting unwanted signals from the receptor. taping a piece of foil over that area is perfect. If it doesn't stop after doing these two things you'll probably need to take it to a shop.
4) If this does stop it, then look for unexpected signal sources. Have you added a remote control extender? Added a new device to your audio-video system? Changed to a new remote?

I hope this helps. Joe