Blank iPad not restoring, Serial Number n/a, "Waiting for iPad". Help?

Blank iPad not restoring, Serial Number n/a, "Waiting for iPad". Help?

Aunts 64GB Wifi iPad2 went blank, IOS unknown. Tried other cables and PCs. Antivirus disabled. iTunes recognises iPad2 but serial number n/a. Suggests restore so agree and iPad shows apple logo and progress bar. Progress bar does not progress and iTunes says "Waiting for iPad". Stays that way forever until unplugged when after a few minutes it goes blank again.