I HAVE TO DOWNLOAD YAHOO MESSENGER EVERY TIME I

I think you have installed and running any program like Deep Freeze, which removing the newly installed program after every restart of your PC. I will suggest you to disable any program like that because this type of program use to keep safe your PC.So try disable that. If still not works just go restart your PC as administrator and try ..Hope it will help. For further help please let us know.Thanks for joinning Fixya.

Please don't write in all caps. No need to scream.

No, you don't need to download YIM each time. Why are you doing that anyway? Did someone tell you to do that?'

Launch the version that you have already installed.

FYI: They're all free.