[Mac] Keychain "login" cannot be found/ won't log into iCloud

My mac seems to be on the fritz. It's about two and a half years old. I keep getting error messages saying "keychain login cannot be found to store 423479966 (and others)" and I keep getting a pop up saying I'm not logged into iCloud and when I try it doesn't load, but if I enter an incorrect password it says "incorrect". If I click reset to defaults or cancel it just pops up again a second later. So my Mac is pretty much unusable at the moment since I keep getting these pop ups.