As i understand you have downloaded and installed yahoo mensenger, However its not working.
Please do the following to get yahoo messenger running.
1.First Uninstall yahoo messenger from your laptop.
2. restart your computer. Then check if all the files are deleted from Program Files and also from the registry. If not once again delete all entries of yahoo files.
3.restart your computer. Normally while downloading yahoo messenger, you have to make sure that there is no interruption in downloading. Else all the files dont get downloaded.
4. Normally to download yahoo messenger it takes 30 min to 45 min of time from the website.
5. Use the link below to dowload yahoo messenger. Please use different version of yahoo messenger as per the operating system you are using.
6. Once downloaded please install with all other messenger services exited.
7. Open yahoo messenger and login using username and password.
It will work