I had exact same issue after upgrading through Kies to ICS. There is a known issue within Samsung and AT&T that is bricking these phones either right after they upgrade or within 3 or so days.
Mine was bricked, I contacted AT&T and they said they knew about it these issues and was authorized to send me a replacement phone.
I received mine yesterday and it was flashed with ICS 4.04 already.
Sorry man, you have a brick and you are going to have to contact AT&T to get it taken care of.