Tv is 5 months old sound is good but no picture at all???????

SOURCE: My TV has gradualy developed a blurred picture

guessing this is a rear projection tv. You did not provide a model number. Check the CRT fluid to be sure it is clear and not cloudy. Since you mentioned the problem was gradual over time, I'm guessing it is the fluid. This would be more obvious if you were seeing like a frosted look to the picture or dark areas and bright areas, which are caused as the fluid clouds up.

Your alternative is to try adjusting the focus of each bulb on the focus block of the tv. I think with an older Philips the focus block is in the back of the tv.

SOURCE: After 2years and 9 months the picture went black,

Most likely, capacitors in the power supply are bulged. It is not an expensive repair.