My Samsung Galaxy 2 stuck every time when start up. It looks ok on the beginning, it shows "Samsung Galaxy S II ..." then change display to Vodafone logo then the shows word "samsung" and stuck here forever. It does not respond to any key after that. To shut it down I need to take the battery off. My questions are if I can recovery the operational system or at least data from the phone.
I believe I have a similar problem and shall update this answer as I find more information.
What variant of Samsung Galaxy S II do you have?
These steps could help:
Fresh reboot by pulling battery, SIM card and any external SD card out for a while (some sources I have read say to wait over an hour).
Clear the cache partition (this is safe, no data loss):
Hold power, volume up and menu simultaneously to boot the phone into recovery (for Samsung).
wipe cache partitionusing the volume up and volume down keys, then press menu.
boot-looptag information contains further instructions.
Otherwise, this answer indicated that it should be possible to root the phone and recover data via the Android Debug Bridge (ADB): these instructions should work for the Samsung Galaxy S II GT-i9100 but I have not yet tried them.