My apple ID works fine on my iPhone but not on my iPad?

I lost my charger for my iPad mini so I wasn't able to charge it for about a month (long story). I turned it on today and it asked me to log in with my apple ID. I entered the correct password and I was told it was invalid, so I reset it. I was sure my password was correct, yet my iPad kept telling me it was invalid so I reset it a total of four times. I tried signing into apple ID on my phone and it works just fine. I've been trying for an hour now. Can anybody help?
Added (1). Also, my wifi works fine for my computer but not my phone and its weak for my iPad. I went next to the router because I was trying to sign into on the app store and it won't connect. Ive checked the settings, I've check everything. I turned my iPad off and back on again. I checked to see if I was supposed to be using iCloud. Why won't anything work?

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