Today no signal, yesterday all was fine.
This could be caused by a cut in power to the signal amplifier or to the bel transformer. Mostly these are connected inside the cupboard where the gas and electricity meters are. Check if all power plugs are in and there is no fuse blown.

In an increasing number of cases the supply of TV/Radio signal is not inclusive in the rent. Many people choose to have digital radio and TV (available through Digitenne). In other cases tenants unite and conclude a UPC contract. To check if the bill is paid call UPC at 0900-1580.

A weak signal
In case you share the TV signal with others it could be that someone made a modification to the wiring or switched off the amplifier.
It also could be a problen in one of the plugs to your TV set. A long connection cable should be of high quality (expensive) in the low quality ones there is too much loss of signal to guarantee a sharp picture.
Check above first before calling your landlord. If the problem is caused by your activities or your equipment the bill will have to be settled by the one reporting the problem.