Most likely it's dead or dying capacitor(s) in the TV power supply which are stopping the TV completing its start up routine. Google "capacitor bulge" or "capacitor plague".
As long as this is the fault then the fix is simply to replace the capacitors. If you know one end of a soldering iron from the other and are happy dismantling the TV then this isn't a difficult task for a competent DIYer. But if you have to take the TV to a repair shop then the total repair cost will outweigh the value of the TV... by a lot
Used CRT TVs are pretty much worthless now. Many end up on Freecycle. Those that are sold are advertised optimistically for £20-£50, but often change hands for a tenner or less. Sad, but true.