Note : Put it to DFU Mode while connected to computer and also in DFU Mode your iPad will remain blank or shows black screen. Timing is critical when you put it to DFU Mode, so keep trying until it goes to DFU Mode.
If you don't have iTunes application installed on your computer, download and install it from here : http://www.apple.com/itunes/download/
still not able to restart my ipad have tried to install updates but it is saying that I have an error and it is still asking for a password. I have tried to do your instruction but is still not rebooting the ipad,
having used your instructions I had to restore the ipad and have lost all my photo's and apps have re-installed the apps but not able to get my holiday photo's back. so very upset.Linda