[HELP] Crossfire 16bit messes up my resolution

Okay, so my computer is a windows 8, and it has a really weak CPU, and a weak GPU. I do not have enough money at the moment to afford a new pc right now. However I really want to play crossfire. All my settings are to the lowest and I get around (18-50) FPS with frequent stutters. There is one issue which is that I want to play crossfire in 16bit mode. It works and its not that laggy, however the game messes up the resolution, where its not full screen and instead the game is a tiny box that is located in the top left corner. 32 bit plays in full screen but its not the most comfortable way to play crossfire because of freq stutters. I really need help. Thanks.