I didt know if I post this in right or wrong section, but I need help so urgently.

My son use my old iPad 1 last day and he set a passcode in it, unfortunaly he forget the passcode and the iPad is disabled.
I manage to restore it and try to make it into recovery mode, but I accidently make it into DFU, which is now totally blank screen.

When I connect it to my computer, I can see the device detected and its show a icon in Devices and Printer (Windows 7 64bit), right click-properties on it and it write DFU mode.

I try to restore 5.1.1 with itunes in this mode but error 1603 always show up, just before the error show up the device is automatically undetected by the computer, and I have to press Power + Home for 10s and release Power button to make it detected by my computer again.

I am trying to get out from DFU so that I can go into recovery mode to recover it to 5.1.1

How to do now?

iPad 1, 32GB
Windows 7 64bits