I did the exact same thing. Got my phone rooted, installed ROM Manager and flashed CWM on it. Then I clicked "Backup Current ROM" and pressed okay which made the screen go blank. I have tried everything and the phone refuses to turn on. Tried using Odin and flashing the original Ace Gingerbread ROM which I downloaded but it doesn't work. I'm off today to my network provider to take it in and plan to claim that it simply ceased working, fingers crossed they'll believe.
One question though. I tried backing my current ROM up with ROM Manager while the phone was in normal mode. If I backed up in CWD mode, like I have seen people use across the web instead, would I still have the same problem or could I flash a custom ROM with no problems?
Cheers in advance.