how do i fix a samsung tv ?

It's a BIG question ... You will need skills and experience in electronic fault finding - tools and access to parts - circuit schematics and test equipment.

From what you say I would guess it's got a power supply fault but that's purely guesswork from several year's experience mending general electronic stuff (not TVs).

Consider a replacement TV or a visit to a repair shop.

Good luck...

Peccavi
November 2012