Java can become disabled in your broswer (maybe after a Windows update or other update), so here is how to check:

Please make sure you have checked your System Settings and Browser Settings first!

Internet Explorer users only:

Click on the Tools option...

... and select Internet Options

Now click on the Programs tab...

...and click the button marked Manage add-ons...

...and the Manage Add-ons window will now open.

First you have to click on the heading marked Publisher. This will sort everything based on who supplied the plugin.

The Java add-ons are all published by Sun Microsystems, Inc. so scroll down the list until you find these.

For each Java add-on in the list, select the add-on and make sure that the addon is Enabled

If any are disabled, then this was causing the games not to work, so simply click the button marked Enable at the bottom