problem flashing radio

[AmDD]

i cant seem to flash a new radio to my phone. after i first got the phone i flashed a new rom and radio just fine. i then flashed it back to stock to have us cellular fix it. now that its fixed i have flashed a new rom but the radio wont flash. the phone is unlocked but all that happens is the phone goes into bootloader then the screen flashes once and it just sits there, then i get an error on my computer that i need to check the USB cable. i have restarted the computer, tried different usb ports, and re-downloaded the radio. any ideas?