ipad ios 5.1.1 want restore could not, while reboot loop

To resolve this issue, try using the DFU mode:

• Connect your device to your computer using a USB cable.
• Turn off the device.
• Press and hold the Power button for 3 seconds
• Press the Home button while holding the Power button and hold both for 10 seconds.
• Release the Power button, but KEEP HOLDING the Home button.
• After about 15 seconds, iTunes will tell you it has detected a device in Recovery Mode.
• Restore your device

More info here: https://www.theiphonewiki.com/wiki/DFU_Mode