The tv is on, but the screen is black, no sound, etc.

Are your backlights going out?

Sounds like the T-Con board is toast. You can get a replacement at : TV Parts Universal TV Stands DLP Chips ShopJimmy

If when you use the remote the volume, channel, etc options display on the screen then the TV is for the most part working fine...when that is the case the loss of video us usually outside of the tv - cables - cable box - etc

any display in the corners of channel number av etc ?? if you turn the volume up and down does that show on the display if not likely to be a dead panel

LCD TV?
There are two places to look for the problems, the backlight inverter board and the power supply. Look at the power supply first since it is easier to get to, look for burnt parts, bad capacitors, etc. Look for 5vdc, 12vdc, and 24dvc.
http://en.wikipedia.org/wiki/Capacitor_plague
Please post back what you find.

what is the brand, model? try to be specific if you want be helped!!!

The inverter board has been defected. This cause black on the screen because there is no back light.

Replace vertical ic and caps.

using your remote ,off the close caption. the black rectangular box that you see for the message but since you have message in the box. that why you see a rectangular black screen.

I had the same exact problem.
I removed the bulb and cleaned it. There is a small screen at the top of the bulb and it was covered with dust. Once it was cleaned I replaced the bulb and it solved the problem.
Thanks to those who posted the solutions