IPhone :: Loop Even After Restore - Jailbroken

Yesterday I locked it during a meeting, and it froze shortly after I unlocked it a few hours later. None of the buttons would respond, so I decided to try the hard reset of holding the power and start buttons together for 10 seconds. It turned the phone off, but it will not reboot.

Instead, when the phone is plugged in or reset, I get the Apple logo, followed about 2-3 minutes later by the time circle which freezes as soon as it appears. The phone stays this way for 10 minutes or so, until it resets itself with a black screen, followed by a red bar battery symbol, and then the Apple logo followed by the frozen time circle.

I have tried all of the standard reset strategies (pressing both buttons, tethering while the computer reboots, holding the start button while it is plugged in, all with and without the sim installed) and nothing has gotten it beyond the loop.

The phone will go into DFU mode, but I am worried about a system restore as I am under the impression that even if it works, it will mess up my ability to re-Jailbreak it as it will upgrade the firmware to the latest version (which I have been scrupulously avoiding until now). Maybe at this point there is nothing to lose though.

I have an Apple store nearby, but I am reluctant to take it there due to the Jailbreak (although I don't know how they would know given the state that the phone is in). I would also hate to have them replace the phone with a replacement that has the new bootrom that can't be jailbroken (or have they now managed to jailbreak these too?).