InsaneMatt

Artifacting isn't just caused by overheating, but is the common cause. Your card may not overheat while playing one game, but could while playing another regardless of graphical detail. It's to do with the optimisation and how the game interacts with your card. If you're running Windows 8, I guess the new 'Start Screen' could also cause artifacting if it 'overlaps' the borderless window.

That looks like artifacts to me. It's typically caused by overheating GPUs and isn't game specific, however updating drivers sometimes helps due to changes to fan control.

That's not an issue with your 'installation' of phpBB, but your configuration of 'php.ini' (the 'settings' for the PHP service for the website). Edit the 'upload_max_filesize' value to 1024 MB for 1 GB; you'll likely have to do this via SSH access.