Hello, I'm Nathan and I will be assisting you today. Please remember to rate/accept my answer when we have finished. Thank you.
Hi there, sorry to hear you're having trouble with the samsung,
there are several possible causes of this issue, which could be insufficient output from the power supply board, a failing inverter (which powers the backlight), or even a bad panel.
In general, for a set of this size and age, it wouldn't be worth fixing, if you have a local shop do the repairs, you'd typically be in the $300+ range, and as a rule of thumb for sets 42" or smaller, or more than 4 years old, repairs aren't practical.
If you wanted to try fixing it yourself, you could expect to be in the sub $100 range to buy a new inverter board for example.
Before doing anything however, I would suggest you call Samsung at 1-800-726-7864 because this particular model (depending on the purchase date) was covered by a class action lawsuit that stemmed from faulty capacitors in many tvs they made. So if you have a chance of getting repairs covered through them, that is your best bet.