Why will my iPhone 3GS Will not power on after dfu mode?

i have an iPhone 3gs that works . i just jailbroken it and it was tethered on ios 6.1.3. well anyway imy phone accidentily rebooted and i couldn't access cydia. well in an attempt to fix that and boot only from redsnow a passcode was on that iforgot to take off. so when it got to rebooting device it just hung there and it showed my phone in dfu mode but i was unable to take it out. Now it won't turn on or be read by itunes or my computer at all. tried several usb ports and usb cables. Please help.