Mitsubishi LCD HDTV LT-40153 lost all sound... less than a year old

I don't think this to be rectified with a factory reset. Check its backlight inverter board.

Check its speakers. If found OK, check and replace the audio output card. Visit the site named 'Electro-help' for more details. Check this link and select the site named above. View it in 'Flip card' option, which can be selected from the drop down box menu by the [Sidebar] tag, at the top left corner of the display window. It will make search easy. Some times, the ads attached with each posts, both at the right and bottom, might help you to find the availability of spare parts. There are more than 750 posts to different brand TVs now.

Your diagnosis is correct.

Does it come and go? I would try reseting the ribbon cables between the LCD panel and the T-CON board first.
The Flexible Printed Circuit BoardS (FPCB) are ultrasonic welded to the LCD TFT panel, they are not SOLDERED on! The connections do get bad due to very delicate nature of how the LCD panels are made. You can also try squeezing the around the top area of the screen where the lines are to see if the lines go away.

Basic LCD monitor and TV troubleshooting guide:
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide
http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting
Failed TV and Monitors: http://s807.photobucket.com/albums/yy352/budm
Learn about bad caps: http://en.wikipedia.org/wiki/Capacitor_plague
Parts: www.shopjimmy.com
Capacitors kit: http://lcdalternatives.auctivacommerce.com/Default.aspx he can make you a set of caps.
Or www.digikey.com, just make sure to use caps with low ESR, 105c, high ripple current and long life rating such as PANASONIC FM or FC series.
Please post back what you find.

The lamp LED indication flashes?When was the lamp replaced?The lamp has not been replaced 1 1/2 or 2 years.The lamp life is over.Require a new lamp.

if your tv is less than two years old mitsubishi will cover the repair 1800 332 2119

Ur power ic inverter board is dead.
U need new one.

I assume your Misubishi is not close to anything electrical. However, it sounds like you have had an interference for some time. This will ineviteably cause the HDTV LCD to collapse. LCD's don't respond well close to heat. Is there a vent close? LCD's do well in a properly vented area but with all this said.......they will pick up interference from anything electrical. A few questions to ask ones self........are there any wireless devices or chargers close to the LCD? Might there be an oven, a/c unit or other wiring with 220 volts anywhere close to the LCD such as in the wall?
The Mitsubishi LT is a very reliable, multi component ready set that allows great viewing with surround sound. However, stop and think about this interference. It is not something in the unit. It is an interference. Look hard and when you've discovered it.....you won't believe how crystal clear this set will be.
Let me know what you find...Thanks for using Fixya and add any comments that may help us help you.

Similar problem with an eleven and a half month old LT-40148. Approx. 1 inch vertical banding line on left side of screen on all inputs. After about two weeks, same problem on the right side of the screen.

Fortunately this occurred two weeks prior to the one year warranty expiring.

Called Mits customer service and they referred me to an authorized service center who I happened to have dealt with before.

They picked up the set. The front panel (LCD screen ) had to be replaced. Set was gone for two weeks as parts were not in stock. There was no charge. I hope this screen last more than a year.

This problem is covered by Mitsubishi even out of warranty.