If you can, then get hold of a 1 or 2GB micro SD Card and try the flash on that as smaller cards are always recommended for flashing over bigger size cards.i have similiar problem. my usb port is broke and need to return. when i transfer the ruu signed.nbh file to sd card and change name to leoimg.nbh. then power up the phone with volume button down, the tricolor screen comes on and for a milisecond the gray screen comes up but then reverts back to tricolor and nothing happens. i have tried 2 different 16 gb cards with same results, i have even tried it on 2 different hd2s. maybe its the stock rom i am using to get the file from. can you post link to a known working stock rom. any suggestions would be greatly appreciated.
Which stock Rom did you download? What version of HardSPL do you have on your phone? Enter bootloader to check the version. Any Rom should flash via micro SD Card as long as you have HardSPL.
Mark.