Im not sure if it should be in the general one or something, but anyways: Mage apprentice died, and now i can't get the ones att the university to follow. DB murderer fell of a bridge, died, and became resurrected somehow, and refuse to follow. KotN guys just don't follow me.

God bless the adoring fan

A lot will depend on why they died. IIRC if you did it (even accidentally), then you are ejected from the faction and have to do a reinstatement quest to get your rank back. Look in your journal to see if you've been thrown out of any guild/brotherhood etc. recently. You may not even have to kill them for that to happen, but a subsequent death could have covered up the "crime" that did so.

DB murderer fell off bridge in skingrad castle. Mage Apprentice got killed by a raged guard. KotN, guys didn't die, but I recently had Lathon to follow me.