I am not able to use voice at all, I also noticed I cannot make pc to pc calls. I don't know why. Please help me. Thank you All!
If you can't use voice chat in chat rooms then it's because Yahoo! is tampering with their default voice control server pointed to by vc.yahoo.com. There's a simple fix to edit your HOSTS file and change it to map vc.yahoo.com to a different (working) voice control server so you'll be able to obtain voice in all voice chat-capable rooms and in all voice conferences. This is completely Yahoo!'s doing, it's nothing YTK is responsible for causing.
As for your PC to PC calls (voice and video), you'll want to set a working server (many of them are dropping and having session instability issues). I've found quite a few that work perfectly. You can use the server and port (port doesn't really matter, you can set it to whichever) with the following settings below to likely fix your problem:
Make sure to uncheck "Disable Peer-to-Peer PC Voice Calls" like I have it in the above screen shot. This option will sometimes cause an incoming call to be dropped immediately upon accepting it but will work fine for making calls to others. You can open up YTK's event logger when signing in and keep it open to see if your PC Voice Call connection is stable, you'll notice if it's not (it'll keep reconnecting).
The easiest way to check your PC Voice & Video Call connection status is from within your Messenger buddy list window. After you sign in wait a couple seconds and then click the "Y! Voice" toolbar button's down arrow directly to the right of it. If you see the "No Incoming Calls" option item greyed out/inaccessible then currently your PC call connection is not established.