I nuked my 8100 awhile back...reboot loop... and the Device Manager connection fix didnt work at all. (wouldnt turn from COM1 to Unrecognized PIN) It would just keep rebooting...what I did was keep the phone busy as soon as it fully loaded, right before it turned off and on again. I kept pressing the Hang Up button once a second. It connected to desktop manager, i ran the apploader and reinstalled the OS.
Note: I did keep pressing the Hang Up button once a sec until it deleted and reinstalled, then reached Device Initialization. (just out of fear) But it worked!!!
I was frantic at first, thinking I'd never get it to connect to reinstall... but it all worked out!
actually, you can do this without hitting the hang up button. i learned this years ago with the dreaded "app error 523"
-pull battery.
-reinsert battery (starts to boot up)
-immediately connect USB to desktop manager
-During some part of the boot, but before it is finished booting, the desktop manager will recognize the PIN
-as soon as the PIN is visible, reload the OS as fast as you can. dont worry that your BB hasnt finished booting completely, in fact you WANT this to happen so it wont go back into bootloop
-the reload of the OS will actually STOP the reboot process