i got gta 4 the other day, and was playing online fine, now for some reason i cannot. my social club and windows live id are linked, but when in game, and open my cell phone, the multiplayer option is empty, and when trying to invite a friend to play the Invite to game button is greyed out.. i have changed nothing in my network or game that i know of

pc version btw

try creating a new profile and check windows firewall isnt blocking GTA

check your net connection, clean the ports