First of all congratualations to your first post.
- take a SD <= 2GB
- download ROM from HTC homepage
by entering your HD2's serial number
- connect your SD to your PC by using a card reader
- format your SD by using to FAT32
- extract your downloaded ROM file by using 7-zip or something similar
- copy the RUU_signed.nbh to your SD
- rename RUU_signed.nbh to LEOIMG.nbh
- power off your HD2
- insert the SD
- press and keep pressed volume down button while you press power on button
- release buttons after you see boot screen
- follow the instructions you see on your HD2
But, don't forget: be sure your HD2's battery is fully charged, at least > 50%!
I hope this will do the job...
... if not, because you have HSPL on your HD2:
- remove HSPL first and switch back to original SPL