Hi the problem you are having will be with the starter located on the circuit board
where the power lead attatches to the telly thiss will have a thick black wire coming from this to the screen.
To replace this you will need special equipment and i wouldnt advise doing it yourself
as the telly is still live up to 2 days after it is unplugged from the mains.
As for the cost of the repair you will find it cheaper to buy a new telly as when the things go wrong like yours you tend to solve one problem after another so it would be best to replace the whole telly its just not worth repairing yourself.
If you wanted it repairing then goto a small repair shop as they are glad of the work and tend to charge alot less than bigger shops.
Please dont attempt this yourself unless you have been trained to read schematices.
Its not worth electricuting yourself by removing the case as their is no easy fix to this problem this is a common problem with all tellys of your type this happens to them all after a certain time so its not just your telly ive had it happen 3 times.
The first time i done the repair as i have been trained to do this type of work but i found i just kept getting problem after problem so the next 2 tellys that went wrong i just scrapped it really is not worth doing.
Sorry i couldnt give you good news hopefully you wont give me a bad rating but if their was a way to solve your problem i would advise you on it but their is no easy fix. sorry