If you already have a Yahoo! ID then you're ready to play Yahoo! Games. There is no need to sign up more than once.
If Yahoo! Games isn't working on your browser, it is most likely because your browser does not support Java and JavaScript. If you have Netscape 4+ or Internet Explorer 4+, make sure that Java and JavaScript are turned on.
For more information on enabling Java, please visit this help page.
For more general information on what computers are compatible with Yahoo! Games, please visit this help page.