[8125, K-JAM, P4300, MDA Vario Software Upgrading] Zzan:
If it was a G4...

If the IPL/SPL before you started had .0001 on them then you have flashed an incompatible bootloader into your G4 device and have bricked it.

If your device was 1.03 to start with then it is a G3 and you flashed a 2.xx rom into a 1.xx bootloader which again doesn't work (G4 safe roms do not include the bootloaders.) In this situation you can recover your device by installing an official 2.xx carrier rom into your phone. And never mix bootloaders again :) Once this is done if you are CID unlocked then you will be able to install a custom 2.xx rom of your choice.

G3 and G4 bootloaders are not interchangeable. More G4 phones have been bricked on this forum than really should have been for this very reason, read, read, read and when you think you have read enough, read some more. If you have a G4 device the only way that I have read on these forums to CID unlock was to pay a fee to a website to do it for you - Which many people have done and report that it works well.

If your device was a G3 to start with then you might be able to re-flash an official carrier rom (from your carrier) into the phone to revive it. Check their customer service/support website for that information on where to download a release. If you are a Cingular customer you can download this rom from the HTC website (don't know about other carriers)

Things you really should know before you flash:

1. Is my device a G3 or G4?

2. Is my device a G3 or G4?

3. Is my device a G3 or G4?

4. Is my device a G3 or G4?

5. Am I willing to have a failure that will leave me with a worthless piece of electronics?

6. Do I have a real NEED to upgrade or change roms?

7. Have I read and understand how to unlock my phone (if not going with a carrier rom from the carrier to which your phone is locked.)

8. Do I know how to boot into bootloader mode?

9. Do I have a backup plan for re-charging the battery if it becomes discharged completely -- Shouldn't be necessary but lots of people including me have made a mistake and gotten their phones in a state where it will not charge.

10. Do I understand how the flash process works, where will it pause, how long will it pause, can I go without my phone for this period of time?

11. Have I spent a good deal of time reading as many threads on upgrading/flashing/unlocking/identifying as I can in a 2 week period. If you just got your phone.

12. Have I backed up all the information on my phone that I may or will need once the flash is successful?

13. Have I read the entire thread on the rom that I wish to install to see what issues others have encountered while downloading, installing, running/using and how they fixed or worked around them?

14. Is my device a G3 or G4 and do I have the appropriate rom?

Really, the people here aren't trying to be rude or jerks, the problem is that most newcomers to the boards jump in with both feet without reading all of the very well written tutorials and fully heeding the warnings included with them, and invariably they all ask THE SAME questions, because they either A. don't know how to search (yes, we all know the built in search function leaves alot to be desired. -- Use Google) B. are too lazy to search/read and want to be spoon fed. C. really believe that they are the first person to have said issue.

The sad fact is that most people that brick their phones have no good reason to have upgraded in the first place.

I hope your phone was indeed a G3 to start with and you can revive it with a carrier rom. If not then this is a very expensive lesson, and I am sorry that you had to learn it like so many others this way.