i can"t log in my yahoo messenger?

Verizon closed down Yahoo Messenger more than a year ago, so this should get you to see why you couldn't log in to it.

Instant messenger no longer exists. It was closed in July 2018: https://help.yahoo.com/kb/SLN28776.html

It still exists?

Verizon terminated Yahoo Messenger on July 19, 2018 is why. That was over a YEAR ago. We were given 3 months warning. Personal emails were terminated by Verizon, NOT Yahoo, over 2 YEARS ago. Instant messaging was terminated by by Yahoo 5 or 6 YEARS ago. WHERE have YOU been..