Shows that Pin is incorrect even after entering the correct pin

I have not turned on this iPad for close to 2 yrs and tried to turn it on after charging. I remember the pin very clearly and have been trying to open it but it won't open with this pin number. I don't have any other apple products and haven't linked this device to anything else because I was only using it for a very specific purpose. And now I want to be able to carry it with me but am unable to unlock it. Please Help