When you attempt flashing, do you do it from the device already booted into windows mobile or direct from bootloader?
Which ever way you have tried it, try ther other way.
Not teaching you to suck eggs but just in case you dont know.... To get direct to bootloader hold camera button and soft reset with stylus whilst holding camera button down and the tri colour screen should appear.
With device at the bootloader screen, Can you confirm that you hear the windows "noise" when you unplug and re plug the USB cable just as you would when plugging and unplugging the device normally. This will determine if the device has connection at the bootlaoder stage.
Phone - TYTN II
ROM - Duttys wm6.1 (23rd March)