Screen Frozen of Insignia Tablet

My Windows tablet Insignia Flex 8 NS-15MS0832B-C has error SECURE BOOT VIOLATION INVALID SIGNATURE DETECTED, CHECK SECURE BOOT POLICY IN SET UP

OK

but screen has frozen and touch screen not working. So not OK touch screen working. Many times tried by pressing and hold power button to reset but every time same error on frozen screen. How can I boot my computer