Hello, I'm Shahid.Sorry to hear that you're having trouble with this but I'll do my best to help.
Flashing power light is indicating an error code so please count how many times it is flashing pauses for 3 seconds and repeats the blink pattern and post that info here to troubleshoot the problem.
Also, can you recheck TV model number that seems incorrect/ missing few alphabets/ digits?
TX-P42C10B is valid model, before there was P missing in number.
7 times flashing light is an error code that indicates SC board failure, this board is located on left side if you're looking at TV rear and back cover is off. Need to replace SC board to resolve the problem. Please click following link to view SC board image and part number info that can be used to search/ google it to get replacement SC board better price info to order it if you have plan to do-it-yourself..
I hope these info will help. If you have any additional questions, feel free to ask. If you're satisfied, please rate me a 5-star at the top of your page. Thank you.
You can expect $250 plus repair cost from local TV repair shop. Question page shows you're in UK so that link may not work, let me post different supplier links..
You're welcome, if you have any additional questions, feel free to ask.
Wish you good luck~