My glowworm 100e boiler is broke and im freezing please help!?

Hi, I have a Glowworm 100e fanned flue combination boiler and it won't work. We turned it on yesterday, it sounded like it was going to come on then made a strange noise and went off. The pressure dropped to 0 so we followed the instruction mnaual and managed to get it back to 2 but there is a flashing red light next to a picture of a half full radiator and the heating and hot water will not come on. Please help, its as cold in my house as being outside!!