Windows crashes after graphical errors

Recently, my PC has been giving me various graphical errors then automatically shutting down. After restarting it works fine for a while, then it starts all over again. At first, the errors are small and almost unnoticeable such as some random text on a webpage becoming stretched or skewed. Shortly afterward more and more appear and suddenly the whole screen is just a mass of color blocks and Windows crashes or restarts. Windows suggested that I update my video card drivers to solve the problem, which I have, but hasn't fixed anything. The card I'm using is a Radeon 9800. Can anyone help?

Heat issue.

Probably the fan on the card failed. Open up the case and poke at it, but be careful not to hit the electronics.

ARTEFACTS.

unplug then plug RAM and Graphics card.
worked for me before.

9800 is notorious for causing this problem.
I had it once, it made me feel itchy.