Window putty works well on older windows. Just put the putty between the pane and the glass. This should seal the window and keep from water coming in.
Use some window sealant putty and apply it all around the window pane the use a finger and run it round were putty is applyed to give it a smove rounded in effect then use a damp cloth to clean any putty left on the window pane.
Maybe you need to reseal or caulk around the window pain. You will probably have to clean the window pain and scrape off the old cauk, if any. Then reapply the new cauking agent.