Windows 10 will not let me sign in to my account to access my computer

Bought a Dell in August with Windows 10 installed on it. Suddenly in November when I booted up my computer instead of letting me sign in I got a box with the following message:
We can't sign into your account. This problem can often be fixed by signing out of your account and then signing back in. If you don't sign out now, any files you create or changes you make will be lost.
Of course I signed out and then the same box kept popping up. I can use my computer but any gaming etc. I do isn't saved and every time I fire up the computer I start all over. So... I literally reinstalled my operating system and within days it was right back where I started. I am not very computer literate and I need help.