your screwed!! that is what happend to me. i used an app ( i cant remember witch one) and that happend to me. i was able to return it to get a new one. then i used iliberty ( a whole lot safer).
hi pal make sure your sound is on on ur computer, press and hold the power and home buttons togeter untill u here the beep, now let go of the power button but keep pressing the home button until u here another beep. I've always managed to get them back in DFU no matter what condition u get them in.
if the above fails make sure the phone is off and not pluged in the computer open itunes then hold the home button for a few seconds and plug the phone into your computer and wait for the dong sound then restore