I'm having difficulty getting some java based apps running on my computer. It's a MacBook, generation just before the most recent one (about a year old), and I've had the latest version of Mac OS X with every software update.

I can't get, for example, RuneScape - the massive online adventure game by Jagex Ltd. to load the applet beyond the "play free" or "play members" buttons. My sister has an identical computer to me, and on her's a certificate of trust appears, when you trust the certificate it proceeds to load. On my computer there is no certificate, at the bottom of firefox the loading bar says "Done" and the screen is left black and unloaded.

I have tried it in Internet Explorer, Safari and Firefox. None of them work, Safari's black loading screen has a refresh symbol with the java coffee cup in the middle of the arrows. I've fiddled with all security and certification related options in applications/utilities/java, rebooted, done everything in the recommended guides, updated my OS... yet the problem persists.

The strangest part is it works with no problem on my sister's computer, and I can find no differences in settings.

Any help would be greatly appreciated.

EDIT: I think this is in the wrong forum, sorry. If required should it be moved to an appropriate section?