As grog68 said, until you have a picture showing on the screen, you will not get a signal level.
Have you changed anything on the box at all - any settings or anything or anyone in the house who may have?
Maybe V*rgin are doing some work in the area?
Do you have any V*rgin services (legit) like internet? ... if not, it's possible they may have unplugged you at the cab (unlikely but possible).