Sounds like the standard symptoms resulting from the bad capacitors which plagued a number of Samsung TVs.
There was even a lawsuit that required them to fix the issue free-of-charge -- but it's no longer in effect.
If your TV matches any of the following models, then it's most likely what's causing the issue ...
... even if it's a different model, it could still be the direct cause.
It's not horribly expensive to repair, and easy enough to do for anyone who's decent with a soldering iron.
- First, the back of the TV will need to be removed.
- Verify that there are one or more bulging capacitors and identify the values of them.
- Order capacitors with identical values online.
- Then, change them out.
Once they're replaced, it should work like new again.
Best of luck.