Answer
yahoom~1.exe - application error
the application failed to initialize properly (0xc0150002).
First, quit re-installing it. You may be creating more problems. If you re-installed many many times, you should take a few minutes to clear all the failed attempts. If you have a utility that will clean up your hard drive of unnecessary installation files, then this would be a good time to use it. Now, tell me why can't you log in? Is someone or something preventing you from logging in? Did you receive a message that stated "You can not log in"? The more information you give, the better.
What errors are you receiving when you try to log in?