How to lock iPad - iPad Apple Tablets & eReaders

https://www.lifewire.com/remove-icloud-activation-lock-from-ipad-4586831

https://www.businessinsider.com/how-to-bypass-activation-lock-on-iphone-ipad

If it white screen you are screwed if you do not no the Apple ID

if you can access the screen you can google check Apple ID then type the serial number to heck if it iCloud lock you can find serial number or imei number back of the iPad or in sim try if it's 3G iPad then type in and see if the iCloud is locked or not if it's not you can restore Ipad by iTunes on your computer turning the iPad off by pressing holding the power button and in-certain the charge till iTunes logo pop up on your iPad and then on your computer then restore the iPad

Is there anything wrong with the passcode? If your iPad is locked and you forget the passcode, please follow the steps below to unlock it.

1.Connect your iPad to your PC or Mac.
2.Select your device in the iTunes sidebar, and click the"Summary" tab.
3.Click "Check for Update". iTunes will show you if there any new version of iPad software is available.
4.Click "Restore iPad". You can finish the restore process by following the instructions given. During the process, a recommend that tells you to back up your files will be given. You can restore your data after the process is complete.

Now, you must have restored your iPad.
Note: Even you bring your iPad to the Apple service center, Apple staff also need to restore your iPad to unlock it. That's to say, you need to erase everything on it.

http://www.leawo.org/tutorial/forgot-ipad-screen-lock-password-how-to-recover-data-from-locked-ipad.html

When you've forgot the lock screen password of your iPad tablet, you get 6 tries of the password entering. After that, the only way you could do is restore you iPad to Factory Settings, which would then no doubt delete your data and files on iPad. The lost data and files would not be backed up on iTunes then. In such case, the only way you could recover data and files from locked iPad is to use 3rd-party data recovery software app. Feel free to read this article to know how to recover files from your locked iPad.
Forgot iPad Screen Lock Password How to Recover Data from Locked iPad

In order to unlock an activation locked iPad, you need to get the activation lock turned off. If you have iOS 8 or above, watch this video on how to do it.

I would go to an Apple Store and ask for help.
kolbrun

If 'Find My iPad' is on, you can use this to remotely lock an iPad, usually because it's lost.

When you've forgot the lock screen password of your iPad tablet, you get 6 tries of the password entering. After that, the only way you could do is restore you iPad to Factory Settings, which would then no doubt delete your data and files on iPad. The lost data and files would not be backed up on iTunes then. In such case, the only way you could recover data and files from locked iPad is to use 3rd-party data recovery software app. Forgot iPad Screen Lock Password How to Recover Data from Locked iPad

Try pressing the home and lock/unlock buttons on your iPad for about 10 seconds. The iPad should restart and soft reset. This won't delete anything. It will just force it to restart.

If you've got a locked up iPad app or otherwise misbehaving iPad, and want to reboot / reset your iPad, simply hold the sleep and home buttons together until the iPad restarts.
You'll see the shutoff slider come up first, but just keep holding. The screen will go blank and the Apple logo will reappear as the iPad reboots.
Note: this does not reset any data on your iPad. This is just a restart, equivalent to rebooting your computer.