contacts offline - aim or ichat problem?

I'm having difficulties with iChat and AIM. Whenever I login to my account, all of my contacts are listed as offline, even if that isn't really the case. And I did a test and realized not only can I not see my buddies, but they can't see me - even though my computer says I'm available. When I tried to get on AIM express to see what happened, I had the same problem. Is this an AIM problem or an iChat issue, and does anyone know how to fix it? I've looked all over for a solution and haven't found one yet that works.