1999 FORD Expedition wont start

need help my 1999 ford expedition wont start it cranks but wont start. The
odometer has dashes all the way across and the theft light isnt blinking. we
had though it might of been a theft issue but since the theft light wasnt
blinking we couldnt get a code so we tried replacing the PCM relay but that
didnt work either someone told us it could be the PCM MODUAL "computer"
but we are hoping it might be something else as of the only way to replace
the modual is to pay alot of money not worth the fix please if anyone knows
what else it could be that would be awesome and if you think that might be
the problem let us know we need as much advise as we can get