[Desire HD Q&A, Help & Troubleshooting] sashank:
Ok, it's like this. The way most people get root and recovery (and the recommended way) is through the AAHK. It gives you an option to flash a completely unlocked ENG S-OFF bootloader, which allows recovery to flash the boot image to the /boot partition too. This is what makes the phone start, otherwise it'll be stuck at the HTC Quietly Brilliant screen. Most people will tell you that you should run an RUU and get back to locked bootloader state and then run the AAHK. This IS the preferred method if you want to have a fully unlocked phone, but if you're finding it difficult to do, don't do it.

You've unlocked the bootloader using the htcdev unlock tool. What that does is partially unlock your bootloader. It allows you to flash zips to the system partition and data partition, but not the boot partition. So what happened to you was that you flashed CWM recovery, used it to flash a ROM, but it didn't boot - this is because though the ROM flashed fine, the corresponding boot image for the ROM was not flashed, so the ROM cannot start. The main headache with htcdev method of unlocking is that it leaves you with a S-ON bootloader preventing the flashing of boot image directly from recovery. You will need to flash it manually each time you flash a ROM.

The procedure to do that is -

1. Download the attached zip file, extract it to Desktop or wherever you want using 7-zip/WinZIP.

2. Open the ROM zip file you downloaded. Extract boot.img from this zip to the previously folder which you just extracted in the above step.

3. Turn your phone completely off (pull out battery). Then hold 'volume down' while pressing power and continue holding it till you see a white screen with 3 green skateboarding Androids. This is the bootloader.

4. FASTBOOT will be the first selected option in the list. Press 'Power' to select it. Make sure that now it shows FASTBOOT in red under the initial green text.

5. Connect your phone to computer. See that the red FASTBOOT changes to FASTBOOT USB.

4. Open the adb_fastboot folder, open 'Start here.bat'. It will open a command prompt window in that folder.

5. Type 'fastboot flash recovery recovery.img'. You only need to do this once. It will flash 4ext Touch Recovery, which is better than CWM (thanks to madmaxx82 for the awesome recovery).

6. Type 'fastboot flash boot boot.img'. You will need to do this everytime you flash a custom ROM, but before you do so be sure you've copied the boot.img from the ROM zip to the adb_fastboot folder.

7. You should see some stuff like 'Sending data... data sent successfully'. If there's any error at this step report it here.

8. Once it has done everything and displayed a successful confirmation, disconnect phone.

9. Hightlight BOOTLOADER and press 'power' to select it. Press 'volume down' to highlight RECOVERY and 'power' to select it.

10. Once you're rebooted into 4ext Touch Recovery, go to 'install zip from SD card', browse for the ROM zip file in your SD card. If you haven't copied the zip to SD card, go back a step, connect phone to computer, select 'toggle USB storage' and then copy it onto the SD card. Once you have the ROM zip on the sdcard, go to the main screen of the recovery, choose 'wipe/format'->format all partitions (except SD card). Now go back to main screen, choose 'install zip from sdcard' and browse to the ROM zip location, select it and confirm that you want to flash it.

11. When the flash process is done, go back to the main screen of recovery, and press reboot now. You will reboot into the custom ROM.

This is the process to flash a custom ROM and get it to boot properly IF you have unlocked the bootloader using www.htcdev.com. For AAHK unlocked S-OFF bootloaders, you can just flash the ROM zip from recovery. The boot image will be flashed too.