Every time I try to go to Yahoo.Messanger It logs me out saying I am logged in on another device.I have but one computer?

If you gave him your password and your username for your email account or for your messenger account then he can log in to your account and change the password to one only he knows. If he can get into your email he can read all your old emails. If you use the same password for multiple accounts, he can keep guessing at what accounts you might have and try the password. Even if you have accounts that don't use the same password but use your email address to log into, he can try to log into those with your email address and say he doesn't remember your password and they'll email him a new one.
Sounds like you're screwed. Call your ISP (Internet service provider)

What does it say when you try to login to your Yahoo! email? Try opening it using a different web browser.

Yahoo mail has chat activated and that's why Yahoo Messanger logs you out because you cannot have two instances of it running. To fix this, on Yahoo Mail screen, under Chat & Mobile Text, select Sign out of Chat and it will show I'm Offline. In this way it won't kick you out of Yahoo Messenger anymore.

There could be a few reasons for this, does anyone else have your Yahoo username and password and is logging in on another device??? also, there is a messenger area on the side of some yahoo mail inboxes which can automatically log you into yahoo messenger when you check your mail, and this of course will log you out of your main yahoo messenger, but ethier way check and double check, because if its saying this there is something else logging into your messenger, Do you have Yahoo multi id?? if so it could be that - my advice keep checking all options.

so try to uninstall yahoo messanger, and check for any virus instaled. and reinstall messanger,and test

Hi,
first you properly install the Web Cam Software, then you open the Yahoo messenger and again access the web cam. I hope it will work fine. sometimes yahoo messenger not access to Web Cam, that time yahoo messanger not working properly.

thanks

uninstall and reinstall

have you changed your firewall settings recently?
Maybe the firewall is preventing the connection. or if all is not working, try uninstalling the messenger and installing it again.

click to log on to yahoo enter your user id and the click forgot password this will send an email with links to reset your password

clean your cookies. https://help.yahoo.com/kb/SLN27197.html