Have had this happen three times in past few days. Originally used Mac with PwnageTool to unlock with no problems. After a week or two, phone locked up after UNinstalling Winterboard theme.
This time, I used WinPwn to create custom firmware - 750MB partition. That lasted a day and a half and ended up with "no boot" problem after uninstalling another Cydia program. I recreated ANOTHER custom firmware - 800MB - (wanted to change logos), pwned phone with WinPwn again, and synced everything back. Removed a few unused App Store apps, hadn't rebooted yet, and iPhone spontaneously rebooted.... Well, tried to. Stuck at boot logo.
Forced reboot, tried a couple of times before plugging into computer with iTunes open. After about six attempts to boot, finally did. Went into Cydia, installed ONE thing (Flixwagon) and Cydia locked up. Now, after 12 attempts or more to boot in various ways (force reboot not attached to computer, attached to iTunes THEN booting, holding down Home and attaching to iTunes to force restore mode and then canceling that mode, plugging into wall outlet, etc.), I'm stuck.
The boot logo stays at full brightness for about 5 minutes or so and then dims. I usually - when attached to a PC - get a couple of vibrations a couple of minutes after turning on, then a couple more, and sometimes a third set of vibrations. Right now, I can see the phone in iTunes, the logo is slightly dimmed and USB detects when I remove phone from system. I can (sometimes) SSH into the phone in this scenario. But the phone disappears from iTunes and I get a USB Device Not Recognized error when reattaching.
Any clue on how I can restore this sucker and keep it running? Am I doing something wrong? Should I adjust the size of the partition or am I barking up the wrong tree? Is there a trick to getting past the boot logo and getting it to boot in this situation?
UPDATE: While typing the above paragraph, the phone finally booted. All I did was force the reboot while still attached after I plugged it in and got the USB Device Not Recognized error.... I'm clueless!