Tv Techwood

So you have a satellite dish and a decoder next to it

preferably with the decoder turned off
check the card: remove it, blow a bit into the slot, wipe the card on your sleeve, then replace it
check that the antenna is well screwed to the wall and then to the decoder
also check that the cable is in good condition from one end to the other, from the dish LNB to the wall socket in your home and then to the TV: often, the inner core of the cable is fine, but the ground connection is missing when tightening the F connector, which tends to cut the ground and generate unwanted resistance.
once that is done, turn the decoder back on, and of course, choose the correct source on the TV! usually HDMI or
"aux" if using a SCART, depending on how your decoder is connected to the TV.

Hello
you can't "turn off" the DTT

DTT is a signal received by your rooftop antenna (aerial) and then transmitted to the TV via the coaxial cable (the wire) of the antenna
either your television is capable of decoding this signal on its own (MPEG 4 tuner)
or if your TV only has an analog decoder (MPEG 2)
in that case, you need to use a box (digital decoder = DTT) next to it, and connect the antenna to that + of course, turn on this box
what do you have to receive the DTT?