Video Drivers constantly crashing.

Every few minutes/seconds while watching videos my screen will freeze then flash black. Once that happens it's back to normal with a little window letting me know my drives stopped working and have responded (or something like that). I have no clue what to do and i have tried to update my drives and still nothing. I am using Windows 7 64-bit and ATI Mobility Radeon HD 4250 and 5470. I'm not really sure what i am doing if you couldn't tell. So if you need anymore info just let me know.