ichat, and lots of confusion

i got a quick question b/c im stumped on this problem... yesterday when i get home and before i go to pick up my imac, im on my room computer and i have trouble logging on to my chat client aim which is on that computer presently... however i can still get on te internet.. now this morning, i try to log onto ichat this morning, and the internet works and my handle in my room computer works, but ichat doesnt work on my mac any ideas? greatly appreciated. thanks