The first thing to check is whether you have the latest version of Java installed. You can do this at this link. If you do not have Java installed or your version is out of date, you will be warned and given the option to install the latest version. If your operating system is 64-bit, it is recommended that you install both the 32-bit and 64-bit versions of Java, as some browsers run one way or the other, and therefore require the plugin for the architecture indicated.

You can download the different versions of Java for your operating system from this link.