Speakers not working, but cables all plugged in...

Go into the onscreen menu of your TV, find and select the audio options. Make sure the audio out on the TV is enabled (this might be an automatic feature and might not be displayed -it depends on your TV model). Next make sure your receiver is working and (if it is so equipped) make sure your speaker switch is enabled.
Make sure all of your cables are working. You can do this by switching out the cables one at a time for ones you know are good.
Make sure no headphones are plugged into your receiver or the TV -this usually turns off your audio signal to any speakers.
Your TV remote may be equipped to control the volume output of the external audio out signal. Some TVs automatically turn off the internal speakers when you hookup or select an external audio output. turn up the volume on both (your TV and the Mitsubishi).
Does the Mitsubishi work on other sources (DVD, radio etc...)?
Remember to double check your cable connections -audio OUT from the TV to audio IN into the Mitsubishi. Reversed connections can damage your TV and amplifier electronics.
What model is your Insignia? Some are equipped with digital outputs which, if your receiver is so equipped as well, can send surround sound (home theatre) signals to your receiver. These can be orange-colored rca jacks or optical jacks. They do not send analog audio signals.
Once all the cables are double-checked, (double-check your speaker connections!), turn on your receiver, TV and signal source (cable, satellite DVD etc...), bring the volume control (both on the Mitsubishi and the TV) up to nominal levels. You should hear sound.
One more thing:
Make sure your speakers work. You can try them on another amp or simply touch the speaker terminals with a 9-volt battery (the speakers should move in or out depending on the 'phase' of the connection).
Hope that helps.

This could be because the speakers arn't getting a stereo signal, but first, double double TRIPLE check the wires are connected correctly. Iknow it sounds patronising but I don,t know if you are 8 or 80 years old and it's often best to go for the most obvious solution. afer making sure all connections are correct, have a look at the cable to the subwoofer - is there any damage to the cable or does the cable look like it may have been pulled - out from the sub or it's connection at the other end of the cable? Having eliminated the possibility of cable damage (it may be worth cheacking the cable to the pc) check various settings on your pc - are you getting sound from your other two speakers? if you are only getting sound from one of the left/right speakers and you're sure there's no physical failure with the speakers, then it's time to check your software. go to the little speaker ikon at the bottom right corner and right click. Select "Playback devices" select "speakers" and click "test" did you hear sound coming from the left speaker then the right? if yes then you definately have a problem with the sub. if no, click "properties" then "levels" and check the balance is set to the middle. If it is, then you should, again, suspect the speakers. Finally check the balance on your media player, if you use windows media player, go to "options" click "enhancements" then look for the balance control and make sure it's in the middle.
Finally, I would like to point-out that this particular speaker system is not known for having a loud subwoofer, put your ear against the hole in it and double check for anything happning inside (a crackling noise would indicate a danaged voice-coil.

Hope this helps.

check your Sound audio option in Control Panel....
check your audio jacks and cables for any cable faults...
check the volume control

Did you plug in the audio cable to the back of the computer? If so, this may have disabled the front audio connections (or vise-versa). Try unplugging the audio cable from the computer (that is connected to the monitor) and see if your headphones work. If so, there is the solution to that problem.

Check the audio connection on the back of the monitor and double check that it is plugged into the correct port on the back of the computer. If the monitor has amplified speakers, it would be a good idea to connect to the 'line-out' connector on your computer. This would avoid disabling your front audio panel.

Lastly, check the volume on your monitor's built in speakers. This monitor can double as an LCD television, so it most likely has a separate volume control (that defaults to 0).

do check cables and plugs, seems one channel is out due to a broken one.
try to double/check with another pair of speakers or earphones, to make sure ti is not the card or amplifier.
if u still have the problem, do come back!

The speakers seem to be muted by default - you'll see that the LED is yellow/amber. Tap the control pod - the LED will turn green and speakers will work. I felt like such an idiot after I spent almost an hour trying to figure this out. (This feature should be more prominent in the manual.)

the problem is your computer may not sense the presence of your audio device, chances are your driver is either corrupted nor not yet installed.
go to my computer then right click go to properties, hardware, device manager, 
under the device manager go to sounds and see if ther is any exclamation icon or anything , expand this icon and see if there is anything you see that has a yellow exclamation or question mark right click that icon and select scan for hardware changes , then update driver , better yet go to sound properties and see if you can roll back the driver, if you have the cd utilities for your computer, you can reinstall the driver again and after all this restart once again your computer
cheers 

You might have to reinstall the software that came with the speakers since you had to wipe your computer clean when the virus was on there. The speakers will not work until the software is installed back on your computer.

Are you sure you are plugged into the speaker output on your computer? Of not try the other outputs, and also make sure the volume is turned up and not muted on your computer, check by double clicking on the speaker icon in the lower right hand corner of your screen or by going to the sound applet in Control Panel.

Have you tried these speakers on another computer or with a CD player or MP3 player? If they don't work with another device either than you know there is a problem with your speakers.

Also make sure that the speakers are plugged into a power source if they require it, most likely they do.

Hey merrybell;

So, you have a flat panel with no sound?

Well, with out Brand or Model let me start here:
1. Unplug 'flat panel',cable box or sat. box from the power source, a/c cord from wall, for at least 4-5 minutes, plug back into wall.
2. Make sure volume level on TV and boxes are turned up, some cable boxes have volume controls.
3. Ensure that speakers are turned on, some 'flat panel's' have options of turning speakers off. Check menu....audio/sound.
4. Double check all cables from 'flat panel' to "boxes", make sure they are secure.
5. Try different inputs and devices (dvd) on 'flat panel' or cables.
6. If still no audio, one the boards may be defective.

If so make sure you call a factory authorized service dealer to service your 'flat panel.

Good Luck, Big Irish, get back if have any more info.