nznew:
And yes, i can receive both digital and analogue channel.
You still haven't said if this problem is happening on Analogue, Digital or both?
If its both then the TV is faulty.
If DVD/Blu Ray and USB playback is OK then it could be a faulty tuner.
What is your signal strength and quality on Digital?
The manual should show how to find check.
It sounds like either your UHF antenna is in the roof space or the co-ax isn't connected to anything up on the roof.
No need to buy a STB and watch via satellite as you have a TV with HD tuner and satellite is not HD. It should work OK in your location.