gta4 bug WARNING!contains spoilers!

[gunstarhero]

WARNING ,!!!!contains spoilers!!! ok i am writing this to warn you about a bug in the game ,i finished the mission where you save your cousin from the Russian's in the warehouse , but before i went into the mission i got a phone call from jeff about his wife(turns out he killed her),i did not go to him and went to save the cousin instead when i took said cousin back to safe house it saved the game then took me straight to jeff and the car cinematic and now it is stuck in a loop ,and because of the way gta4 menus works i can't even use an old save or play multiplayer game ,so warning go and see jeff first ,otherwise you will be like me and wasted my hole weekend off play . i am going to have to delete all off my gta info and start agien look like its the only way i will get to play gta if i dont,anyone else had this problem is there a fix before i have to delete everything.