in order…
Daft as it sounds, make sure the Humax remote volume is at 100% graphic should show on TV screen (sometimes remote gets sat on).
Check scart cable as Barry suggested, if that doesn’t help then reverse scart so what was plugged into the Humax is now in the TV and vice-versa.
Make sure the scart is plugged into the top/upper scart socket on the Humax.
If you have anything with rca audio in then use the rca audio outputs (white/red sockets) on the Humax to check.
If none of the above helps then factory reset without format. If that doesn’t help then I don’t know, let us know how you get on.