Your Store communication <handshake> is locked.
To clear you have to force the application onto the Application bar which you can see by using a four finger swipe up on the screen. The four finger swipe up gesture overrides any status and dialogue warnings on screen.
Try the four finger gesture first and see if you have the iPad settings available to you - if yes, tap it and go to General section - restrictions. locate the sliders for iTunes and Ping (ping will turn off with iTunes. Move the iTunes slider to Off.
Wait a few seconds, then slide iTunes back into the On position. Tap your home button to close, then use the four finger swipe to get at the Applications active bar. Press and hold any icon till they start to wiggle, then using the little icon that appears at the corner of each App thumbnail, tap on them until they all are cleared - you will find that the iTunes is one of them.
When you have finished you can then Press and hold the On/Off button to Power off with the red slider when it appears.
If the Settings icon is not visible to you simply tap the home button once and everything will revert to the home screen and you can access Settings as normal, then go to Restrictions and do the process of shutting off and turning iTunes back on to force it onto the Apps bar as outlined above. Switch off using the on/off button when finished using the red slider.
Next With your iPad switched off, Open iTunes on your PC. Open the iTunes Store page - at the right of the screen is the Links section. Locate and click on Account.
Sign in - if you cannot sign in - then come back here and tell me the process stopped at point A (This is so I know what the problem is)
If you are able to sign in OK, connect your iPad with the USB and switch on. It may or may not sync depending on your settings. When the icon for your device appears right click it and select Reset Warnings
Then using the Menu options at the top of the iTunes page on your PC navigate to the following Edit\Preferences - in the Advanced Preferences box that opens choose the Advanced tab. In that tab you will find the option to Reset all dialogue Warnings. Click on it.
Close out back to the iTunes store Account screen - it should still be active.
Right click on your iPad icon at the left hand side and select sync.
With everything now reset go to you iPad and see if you can open iTunes OK. If the message you got before re-appears come back here and say process stopped at point B.
Regards Ct