message came up ipad not backed up stating this ipad hasn't been backed up plug in and lock and connect to wifi but when i press the ok button not responding- just locked, cannot use swipe to close down and switch off button not responding!!

My iPad is frozen with message stating iPad not backed up. It is plugged in, connected to wifi and I have tried it in locked and unlocked. No response to finger wipe to unlock... or swith off bar at end unless I hold down when an option to slide power off appears but does not respond either. Only other info on screen is a small flower in a box bottom right. If I press button by plug in siri comes up but cannot respond. Can anyone help?