I dont know how old the PC is, and you havent stated what graphics card you have or whether its an in built version on the motherboard. ?
If its an Nvidia set up, then go to there website and download the latest video drivers, along with the latest Direct X version and this should resolve your problem.
If its an ATI version then go to there website.
If you dont know , download the following program ( AIDA 32 ) similar to SI Sandra and this will tell you what video display card you have.Just run the program then click through until you see video display.