I realize this isn't the help you're looking for, but unless you can somehow identify which parts have failed, locate replacement parts and do the job yourself, anything else would be wasted effort time and money. It's almost 14 years old and fixing it will be like trying to fix a 1954 Studebaker.

does anyone else have an idea ho to diagnose this problem?

While sometimes there are common known problems and repairs, 95% of the time it requires knowledgeable troubleshooting of the circuits with test equipment. Other components can also fail as the result of another component failing. Philips/Magnavox has always had an unusually high failure rate. Currently, they do not make any televisions and simply license their name to Funai Electric.

Since most people are not usually in the position to simply run out and buy a new television when their current one fails, I often suggest checking thrift shops - the ones that are run by charitable organizations not trying to make a profit. They have, and still receive almost brand new expensive CRT televisions that people mistakenly thought they had to replace just because over-the-air transmission went digital. I've seen $1500 televisions selling for as little $15!

Sorry I couldn't offer more help.