The problem is that having recovered that data, and having done a factory reset (wiping /data, /cache), the phone still doesn't boot. It goes to the Galaxy S2 screen, and then turns off (not getting to SAMSUNG screen).
So I assume there must be a problem with /system.
Is there a log somewhere on the phone that I could access that might show me what the problem is? Otherwise should I try to flash other roms (or reflash the stock rom?) in the hope that this would resolve it?