No sound on my 56hm66

Ask for a reduction in TV license fee!
Have you tried a game or DVD through the TV? If also B/W then it sounds like colour electronics have failed.

Per the manual, page 2
http://www.manualowl.com/m/Toshiba/56HM66/Manual/33146?page=2

This TV contains several cooling fans to moderate the internal temperature. You may be able to hear the fans for several minutes after the TV is turned off. This is a function of the Quick Restart feature and is not a sign of TV malfunction. You can set the Quick Restart feature to stop the fans as soon as the TV is powered off. See "Setting the Quick Restart feature" (- page 20).

may have got a bad new one or ballast board in set is bad. It powers the lamp.

first place to look is the lamp this set uses, does it come on at all?

My tv has the same exact problem have you figured out what it is ??

you have to replace the lamp to resolve this issue

usually when the lamp is going out the picture gets dark if you are getting a rainbow tint most likely the light engine is going bad.

You now have a defective lamp ballast board. It sometimes is the root cause of lamp failures in these sets. The problem here is that Toshiba does not sell the ballast board independently from the larger, more expensive light engine assy. Call Best Buy back and get a servicer out there. He may have to take the ballast board out of your TV and send it out for rebuilding.

michtech

Sounds like the light engine if it's blowing the lamps. Are you sure all cooling fans are operating?

check the lamp