corresponding folder name is Upload?
your ipad is charged over 20%?
your ipad and computer have secure connection to the Internet, giving you enough time
to upload pictures (how is the upload speed on your network?) and then download?
Are you signed in to the same account?
Did you check settings for icloud control panel and verified that photostream is on on your windows?
Did you try to sign out and sign in, into control panel and are you getting any messages when you do?
Have you tried syncing them from your computer to your iPad via iTunes?
ALso, try taking a new photo with your iPad and see if it shows up in your computer. Photostream for me, is just 'there', not something I depend on, but I recall reading that it's not backwards compatible - meaning it syncs new photos, not old ones. If you take a new photo and it shows up but the old ones don't then that would suggest that is right.