Yahoo can't get sign you in on this device

I can get into Yahoo but it acts weird, and it puts me in a sign-in loop whenever I try to go into a set up e-mail from another site. It used to work on this very same computer, but now, even though I'm already signed in, it just keeps asking me for my password, and none of its supposed help works. I've even gotten the following message: "Uh-oh... We can't get sign you in on this device. Please try from the device you use most. And this is the only device I use. It's very frustrating. I've seen others post this problem, but no solutions.