First, try reseating the lamp. Often times, this can be a remedy. To do this, plug the unit and open the lamp door. Remove the lamp by unscrewing the housing, pulling it out and firmly pushing it back in. Reattach the lamp housing with the screws, and then reattach the lamp door. In short, you'll be removing the lamp, and firmly re-inserting it.
If you're not comfortable doing this, you may want to have a technician inspect the unit to give a full diagnosis.
I have a 50inch Samsung DLP purchased in 2006 which just started having trouble. When I turn it on, the lamp light flashes continually. The lamp seems to be on, the screen gets an ambient grey glow, but there is not picture. When I toggle through inputs, the usual green mode lettering does not appear. I get sound, however my sound is routed from my cable box, through my amp, and out to speakers that bypass the tv altogether. I guess this might be a color wheel problem. Also, everybody seems to suggest replacing the bulb. I'm happy to repair the tv for a couple hundred dollars if I can be reasonably sure that I have diagnosed the problem correctly. But with new tv prices as low as they are, i don't want to do unecessary repairs that wind up costing the better part of a replacement set.