Your going to have to first turn the phone off. I have had this happen a few times and had to do a hard reset each time. I think you can just do a SIM pull, boot it, let it load, undo the battery, put the SIM back in, and leave the back cover off.
My 'Zound just got stuck in a bootloop this morning. I had turned off 4G when I knew I wouldn't have it available yesterday afternoon. This morning the phone was haqving trouble syncing so I did a restart and it went into bootloop. I tried a battery pull, followed by battery and sim pull - nothing helped. It would only get as far as the home screen loading - and I could unlock it for just a moment - before it would shut down/restart.
A quick search found this thread. I thought I would have to do a hard reset but found the post by qschilling (#3 in Boot loop) - thank you, Wanda for the link in your post - and followed those instructions. It took a couple of more restarts, but my Rezound is now back in operation (and will stay in 4G even when I'm not in a 4G area...).