I can't sign in to my yahoo messenger!!!!

Remove all your temporarily files with a program such as ccleaner, or similar. Then try again, if it doesn't work, reinstall ym.

I think, someone might try to lock your account. are you sure you use the correct user name and the password? When I used yahoo messenger, I and my close friend love to lock other account as long we feel right about them. all we have to do is keep signing on your account until it said Lock, then you are not able to get in. let it go for a while and it will release it back once the lock system deleted your name.

this may due to poor internet speed. sometimes it may due to spywares. some spywares in documents and settings folder not allow to connect yahoo messenger. check whether you signed in any other places such as yahoo mobile messenger, or webmessers. if you do please signout from mobile and webmessenger. then try Y messenger

You probably have not signed up or have the wrong password. Make sure you have these. If it doesnt work, try making a new yahoo mail account.