Ok for those of you who really don't know what you are telling people to do please stop. You end up putting them in a place they don't need to be. I know you are just trying to help but he honestly doesn't need to unroot etc to get his phone back working.
For anyone who didn't want to read here are the steps you should have done.
#1. Download Install Android SDK -- with drivers.
#2. Make sure the phone is recognized in Windows.
#3. Use unRevoked 3.1 and root the phone / install the custom recovery.
#4. It will boot your phone into recovery.
#5. MAKE A NANDROID BACKUP BEFORE DOING ANYTHING!!!!
Now we are ready to play with kernels, roms, and modifications.
Now as far as your phone not working with the kernels. Did you follow hydra's instructions on finding a kernel that works?
You want to start with #1 and work your way to #4 until you find one that's stable. So you want to try, in this order,
#1 ,
#2,
http://hydrakernel.net/kernels/hydra_ocuv2_v10_signed.zip,
http://hydrakernel.net/kernels/hydra_ocuv2_ov_v10_signed.zip. If none are stable you want to try the
stock speed undervolt.
Now if you have worked your way all the way back down to the stock speed undervolt and your phone is still stuck in a boot loop then you have an incompatibility with your phone. This could be understood from reading. For instance they warn if you are running Froyo, 2.x radio, .79 hboot, 2.63 kernel you are ok, however you will have stability issues if running Froyo, 2.x radio, .79 hboot, 1.x kernel.......
So now the big question are you running Froyo or Eclaire? What radio version and what kernel?
The plainest simple answer to this issue would be to assume you have the right mix of conditions and simply have a kernel that isn't working. So lets fix it.
#1. Download the
Stock speed undervolt hydra kernel. This works on every phone.
#2. Pull your battery.
#3. Put in the battery reboot into hboot by pressing volume down + power.
#4. Select recovery.
#5. mount usb storage, this allows windows to see your sdcard so we can copy and paste the kernel over to it.
#6. Copy the kernel over.
#7. Unmount usb storage by backing out of the menu in recovery.
#8. Install zip from sdcard like you did with the other kernels.
#9. Reboot the phone.
#10. Keep trying until you find a kernel your phone likes.
Now, next time read. If you would have made a nandroid backup of your phone before starting any of this it would have been a matter of restoring the backup and trying a different kernel.
Now with all this being said, if you are running 2.1 or 2.2 you have an incredibly simple way to fix this and get yourself a stock image!! You lucked up
Stock 2.1 ROM w/ root access.
Stock 2.2 ROM w/ root access.
Boot into recovery do the mount usb storage place whatever file you chose onto the sdcard. Install from zip in the menu, install ROM of choice. Then once booted and verified it works make a nandroid backup BEFORE doing anything else.
Hopefully this gets you back running. If you have any questions ask away!