First you have to determine it is the graphics card or the monitor. If you are sure that it is the card I would open the side of the computer and see what your options are, what kind of slots you have. Some motherboards have slots that are specific for graphic cards, some do not, but there are cards for most all of them. You also need to look at the age of the PC, if it is old than 5 to 6 years, it may not be worth fixing, and if it is a laptop, with the graphics card build in the board, it is cheaper to get a new computer.
Yes, that can be a problem, but like Chris said the monitor can also be a problem. I'm better on the graphics card though. Try adjusting your screen cable.
I get double color and this happens only after using the system for more than 2 hours.Can it be a built in graphics card problem?
What does the colour change to/how does it look? It is probably your graphics card. Mine used to do that.
what exactly do you mean?
your computer changes the monitor colour, you get double colour :S
Are cheap computer turns Pink that means it is an old computer And it is time for a new one!