Try re-seating the lamp. With the unit cool and unplugged, open the lamp door, unseat the lamp, side it out, push it back in firmly and reattach it to the housing. Then put the lamp cover back on and see if that helps.
Sometimes just re-seating the lamp (pulling it out and pushing it back in, essentially) fixes these issues.
It might also be time for a new lamp if you notice that the picture has dimmed. Once you notice it start dimming or you need to turn the brightness settings up, that's usually a good time to order a lamp and replace it.
I bought this tv about 5 years ago. The lamp has never been replaced. Started about a few months ago, the video goes blank about 30 min running. I still have audio going and i can see the lamp is still burning. If i turn it off for 10 sec and turn it back on, it will come back normal for 5 to 10 min only. I read few discussion already and tried to by pass the cable box. Still have same issue. I opened up the back panel, and made sure the cooling fan is running and it was. Shoud I still try a new lamp even if the lamp is still lit anyway ?. Any other suggestion ?