serial number n/a

Hello Community:

Newbie here, I'm using ipad3 + wifi only. currently my Ipad @ IOS 8.0.1, just a minor problem such as fb lag, battery life is fast.

upon reviewing this update, I was convince to Downgrade it back again to IOS 7.1.2., so I did a little bit of research, I backup my IpAd 3 using

my SOny vaio laptop (windows Xp) that's when I Download IOS 7.1.2,.. followed the instruction to HOLD SHIFT then click restore, the look for the IOS 7.

to make the story short, every time I insert my I PAD usb connector to Sony Vaio , Serial Number is n/a, receiving an erysror every time I reslove it.

MY IPAD is has an ICON of I Tunes and USB connector black background.

its been 24 hours now and still I cant find any solution.

help please. thanks

Gelo.matters