With iOS 7 and activation lock you will either need to type in the id and password on the iPad, or login to the account on http://icloud.com and remove the iPad from it - activation lock can't be bypased.
Activation lock : http://support.apple.com/kb/TS4515
The ID that you say that you've changed, that is not the same account that you used for iCloud on your iPad ? The iPad doesn't show in the Find My iPhone section on the the account on http://icloud.com ?
If you can't remember your id then have you got any downloads from the account on your computer's iTunes library : http://support.apple.com/kb/HT1920 ? If not then you could try http://iforgot.apple.com