Help!! GTA4 cannot go into any missions...

[FalconVFR]

im about halfway thru the game, and there are several missions available for me, but whenever i go to the yellow arrows to enter them, i just walk right through... i know this probably means i havent finished my previous mission, but the mission i just finished was 'out of the closet', and i killed the guy i was supposed to... problem is, that in the game i went to call brucie to tell him i finished the mission (game does this automatically) but i was trying to run, and was hitting A really fast to sprint, so it hung up right away... i dont know if this has anything to do with it or not. i can still go on dates, and even did brucies online work, but i cannot access the 'unknown contact' on the pier, or go into any missions shown on the map as a letter. so any help would be appreciated, as i dont want to start the game over. thanks. i did try to save then restart the game, but no luck...