"The Video car is a ATI RADEON HD 5850 SAPPHIRE TOXIC 2GB DDR5" Since you have a sapphire card i suggest you get the latest drivers from www.sapphiretech.com . Pay attention because the 5850 and 5850vapor-x have different drives, your card might have different ones as well.
I have a 5770 and never had any problems with it, i am using 10.5 catalist drivers for it.
Here you go: http://www.sapphiretech.com/presentation/downloads/download_index_01.aspx?psn=0006
Step one: graphic card,
Step two: PCI-E,
Step three: sapphire 5800 series,
Step four: Sapphire toxic 5850 2 Gb version,
Step five: operating system windows 7 64BIT and submit
Download the last 3 and install them. After that let us know if you still have that problem.