Did a couple of google searches, It looks to me like a bad power supply.
People have power up problems very soon after getting a new one.
Backlights take a long time to burn out, 1000's of hours usually.
Unless you leave the TV on 24x7, I don't think that's it.
They probably used really substandard caps in the power supply. This is a common place for their Chinese suppliers to shave a few bucks off the cost.
This trick works just fine for the warranty period if they guess the life time right. In this case they missed it by about a factor of 2. So a lot of sets die after 6 months. This is not the first Dell product with this problem.
If you open it up, I'll bet you find some of the caps are bulging or leaking.
Sometimes a competent electronics shop can fix them. Sometimes the failed caps take out other components that are made of what is known as 'unobtainium' in the business. The only way to get them is to buy a doner set with a different problem, i.e. dropped, and swap parts.
Google> dell w3000 power.supply
http://www.fixya.com/support/t196017-de ... video_just