Could be memory issues, in which case:
 update your graphics accelerator card's drivers

Also:
update Adobe flash
update Quicktime

Inside your OS settings for graphics, decrease graphics acceleration a notch or two.

Use graphics card management application software, and:
decrease size of mipmaps, switch off anti-aliasing, increase texture filtering, and generally do whatever it takes to increase performance and reduce quality, as far as tolerable

Inside your OS, use settings to optimise performance, rather than quality.

Finally, hardware - check for overheating - faulty fan or cooling settings of graphics accelerator card

Eternal Hobbyist