Wirelessly posted (HTC Diamond: Mozilla/4.0 (compatible; MSIE 6.0; Windows CE; IEMobile 7.11) Sprint MP6950SP)
You should be able to flash the shipped exe rom regardless. Put your device in bootloader and it should say serial until you connect the usb and it will change and say usb and then flash the shipped rom. If that does not work then I suggest you try a different pc to flash with preferably a 32bit system. You may have a bad cable as well.
When you put your device in bootloader, what does it say on the screen. You can tell if you are unlocked by the spl. If it says 2.31 or .41 then it is unlocked.
You can also flash the shipped rom from storage by placing the shipped exe file in the root directory of a 2MB or less fat32 formatted sd card and renaming the exe to VOGUIMG.NBH and flash from bootloader regardless if you are unlocked or not.