bootloader problem

Hey guys, I've been looking for answer for my problem for several hours without any luck. When my phone is not plugged to USB it won't even start in bootloader mode nor the hard-reset works. When I plug it to USB then it starts in bootloader mode says Upgrade ROM code error Please try again. This screen shows only for about 2 seconds and the phone restarts itself and does the same over and over ... I'm getting desperate. Does anybody know what to do with this issue?