I’m writing this as a canonical answer so that it can help point others in a direction to help them if they encounter a similar situation
Boot Loop/Failure
If you phone is stuck in a boot loop or it crashes before it gets to the home screen, there are two conditions that will cause this:
- Hardware failure
- Software/filesystem corruption
In the case of hardware, this could be anything from the memory (RAM), the storage (NAND flash) and even the CPU. If this is the case, there’s not much you can do, especially from a DIY perspective. You might have some luck sending it in to a data recovery service.
In the case of software or a filesystem corruption, the easiest fix is to put the device into DFU mode (hold power and home for iPhone 3G) and restore from backup
Jailbroken Devices
The pineapple boot logo indicate that this was broken using the Redsn0w Jailbreak Utility developed by the iPhone Dev Team. In addition to being able to jailbreak your phone, it includes a recovery utility to fix boot problems.
With extensive work by the OP, it was determined that you have to download the correct version of the utility for your particular device. This requires some trial and error. Redsn0w also has to be run in Windows XP Compatibility Mode.