I have a 40 sony trinitron tv once turned off wont come back on

The "D" Boards have been big problem causers in these Set's. Unfortunately they are not available from Sony ( At lease not lately),
and the old ones have needed to be sent to Sony for them to be refurbished. I would estimate the repair to be approx 650.00 to 750.00. This includes shipping charges, the refurbishing, labor, and service call. Having a Sony Authorized Service Facility come out, verify and send it off to Sony is the only way I know of getting it done correctly. Typical turn around time is 21/2 to 4 weeks.
I hope this helps,
Skyassoc