Sharp LC-30HV4U with only steady red lights on Display and AV unit; when pressing vol/chan/power on Display, it will go into "service mode" - what should I check next? and how do I exit service mode?

Hold VOLUME UP and CHANNEL UP buttons in while plugging set into power.
TV comes up in service mode.
Press CHAN + or CHAN - to select an adjustment that you want to change
Press VOL+ or VOL- to adjust

I have not had that exact problem, I'm sure you have tried powering off for more than 10 minutes, for some reason that has alway fixed my issues with the same model you have. Good luck!

Power problem are cause by many reasons, i.e Power supply circuit, Lamp driver circuit and most often the TV detects an error cause by power surges. To protect TV from further damage most LCD TV have protection circuit built internally. If this is the reason of your LCD TV not powering On, an error data must be reset back to zero.
To change data you will need to access the service mode and change the value of lamp error code to zero (0). Entering service mode requires a trained TV technician. Changing data can cause more problem to your television. If you are not qualified to service your television, please do not go to service menu codes. Moreover below are the process, pls do so at your own risk.
* Unplug the TV * Press and hold the {VOL -} + {CH+} buttons located on LCD TV unit (not in remote control) Note: If above didn't work, alternately use (VOL -) + (TV/AV input) buttons located on LCD TV unit (not in remote control) * While holding the above buttons, plug in the TV. * The TV will turn on with the "K" or "K123" appears om screen. * Use {CH+} {CH -} buttons to go and display the service menu. Note: If above didn't work, alternately use (VOL -) + (CH -) buttons. * Search for "LAMP ERROR menu" from the displayed service menu by using "up or Down cursor" from remote control, or alternatively use "CH - or CH+ to select "LAMP ERROR" * change it to zero (0) value, using {VOL+} or (VOL -) on remote control. * Turn the set off to exit the Service Menu.

The problem might be cause by lamp error, need to access the service mode to change the value of lamp error code to zero (0). Entering service mode requires a trained TV technician. Changing data can cause more problem to your television. If you are not qualified to service your television, please do not go to service menu codes. Moreover below are the process, pls do so at your own risk.

* Unplug the TV
* Press and hold the {VOL -} + {CH+} buttons located on LCD TV unit (not in remote control) Note: If above didn't work, alternately use (VOL -) + (TV/AV input) buttons located on LCD TV unit (not in remote control)
* While holding the above buttons, plug in the TV.
* The TV will turn on with the "K" or "K123" appears om screen.
* Use {CH+} {CH -} buttons to go and display the service menu. Note: If above didn't work, alternately use (VOL -) + (CH -) buttons. * Search for "LAMP ERROR menu" from the displayed service menu by using "up or Down cursor" from remote control, or alternatively use "CH - or CH+ to select "LAMP ERROR" * change it to zero (0) value, using {VOL+} or (VOL -) on remote control. * Turn the set off to exit the Service Menu.

this is a inverter board defective, please send to repair shop, for repair.

push vol-, input, and power, at same time. keep push until tv start. Then you will see k123 at your screen. Now push vol-, and chan- at same time. You will enter service mode. Look for "error no reset" change the value to 0.

Look at the power supply first since it is easier to get to, look for burnt parts, bad capacitors, etc.
http://en.wikipedia.org/wiki/Capacitor_plague
Please post back what you find.

It believe your on the right track...

this worked for me before, but now the problem came back after being fixed for months! unplug the two connectors at the back of the tv, the ones that look like computer monitor cables. then go to top of tv and use manual controls, turn off main power, then turn on while holding input and vol down button, a small service menu will come up, use the channel up down button to go to test, then push input button, there should be a box with reset and some number in red. use the vol buttons to reset to 0, then power off.... reconnect the cables and then turn on the tv.

This is just the beginning, it will happen more often and at some point in time you will have the same problem some of us are having, it will click the monitor power light will lite up green and the ACV box light will come on green for a second and then go red again and the lcd screen will go blue. Unit will not power up. I have this problem and it has started the same way, I did the same thing and nursed it for about 6-8 months now no matter what I do it wont come on, I have tried no power for a day, cleaning, banging acv around tapping, slapping cursing and still nothing. So if you ever find this problem I would love to know what the fix is and who can perform it, I live on disability now and cannot afford just to let somebody charge me out the wazoo and say they cannot find the problem or tell me something like it needs a whole new ACV just because they don't know what to do. If I learn anything I will let you know also.