Before you do anything, you should backup the photos.
If you are able to install apps, try the following apps:
a) Google Photos app - you need to manually go into the apps own settings, and enable backup. You probably want uncompressed backup (no quality loss), but this will limit the numbers of photos you can backup to your google account.
You can check that your photos are saved by going to https://photos.google.com on a computer, and use your gmail login/android account login.
b) Microsoft's OneDrive app. You can also tell this app to automatically back your photos up to your outlook.com/hotmail.com/live.com email address account.
Once this is done,
Reboot your tablet into recovery mode, as follows:
Hold 'vol down' and 'power' buttons on tablet
Release 'power' when samsung image is shown
Release 'vol down' when the two icons are shown
Use the 'vol down' to navigate between the icons
Highlight the left icon (box)
Press the 'vol up' to select it and boot into recovery mode
You need to select Factory reset from there. YOUR DATA WILL BE DELETED. If you get "Download mode" instead of "Recovery mode", hold down power to turn off the tablet. Follow the instructions above, but instead of Vol Down and power, try vol up and power.