Have you tried reseating the lamp? Unscrew the housing, pull it out a few inches, and slide it firmly back into place? Often times, this can fix that issue.
My TV seems stuck in a constant loop of powering on until the musical sound starts, then immediately turning it self off. The only to stop it is to unplug it. If I plug it back in, it immediately starts up with the power on/power off thing happening over and over...I've tried to reset it, spoke to a Samsung Tech online, however, no resolution. Any ideas?