My 8100 began reseting this morning. Once it when through security verification it would reboot again & again & again. Nothing I could do would make it stop. Went to AT&T and they couldn't do anything. I followed their advice and downloaded the laster version of Desktop Manager and the Phone software from AT&T's website.
The Desktop manager installed fine. I plugged the phone in and began the update/ installation through Application Loader. Everything deleted and installed but during the 2nd stage of the install (the reboot process) the phone would connect and disconnect. After a few minutes the installer stopped and gave me the following message "Unable to reconnect to the device during a multi-stage load operation." Since then my screen is black and the red light comes on for a few seconds and cuts on and repeats.