start-fuel problem

This 95 Blazer was fine till we got a heavy freeze, 10 below, then won't start. Figured fuel line freeze. Started again after weather broke, ran one day then not starting again. Acts like it wants to start then nothing...2nd crank has no fire at all. Replaced map sensor as indicated by computer..no change. Is there a relay not kicking in, fuel line blockage? Can I blow back thru pump or would that damage pump? Have replaced filter. Any suggestions appreciated, thanks, Steve