Greetings - my gaming pc's been unplugged in the loft for a year and the bios battery looks like it's dead. I can't get to it as it's under the fan on one of the graphics cards. But, I can't see how to remove the graphics card as there are no visible screws, and the plate on which they're mounted is riveted in place. The only things I can see to unscrew are some small hex head nuts at the back. Before I break something, please can someone tell me the obvious? Thanks.