I've been using Ubuntu for many years and have been quite happy with it the whole time. I have an Acer Aspire laptop with an AMD 6850M graphics card. On previous versions of Ubuntu, the proprietary drivers have worked perfectly fine, but since upgrading to 12.04 and then to 14.04 (64 bit for both), each time I try to install it via additional hardware or install the drivers using the latest beta or stable version following the instructions from cchtml Ubuntu will not boot as soon as I restart the laptop.

I've tried doing this on Ubuntu, Kubuntu and Linux Mint and have the same issue with all three distros. Has anyone experienced something like this before? If so, please help :)