I've gone through that.
I've uninstalled itunes, reinstalled itunes, restarted the pc, tested cords (i've 2) and still nothing.
Before, whenever I connected it, Picture Library pops up, trying to see if there are any photo's on it to import. It can import photo's just fine.
I went back in and fixed that so it would stop, but itunes still refuses to see it and there are no third party programs that are trying to open the ipad.
Strange enough it works fine on my desktop pc that's also running windows 8.1 with the newest itunes.
Just had the same issue,
This occured after I upgraded to Windows 8.1
As luck would have it I found the fix fairly quickly, Go to Store then choose "Authorise this computer". iTunes bleats that this computer is already authorised, but the iPad then connects correctly. I assume some peice of information is being wiped out during the upgrade process on certain P.Cs
hope this helps
Go into the control panel (you hover in the lower right corner to bring that up)
Once you get into the control panel, go to programs, add/remove programs. Uninstall iTunes, Apple mobile device service, apple application support. Then go out to apple.com and redownload and reinstall iTunes and try again.