So basically I might fix my pc soon due to its problems described in previous threads and I have a radeon 6990 which I would like to use as a replacement with my current nvdia geforce 8400gs . I would like to know how long can a radeon hd 6990 last and if there is possibility of extending the graphics card's lifespan.
The card will last a long long time if treated properly. Since it is a few years old (model-wise), the first thing I'd do is clean the old (probably dried out) thermal paste off and replace it with some high quality stuff like MX-4. Keep the card clean of dust during use to help keep it cool. Be sure to have good air flow to the card to expel heat. Heat and over-volting will take its toll on the card sooner than most anything else. And lastly, feed it with a quality PSU that is free of spikes and ripple. All this is especially true with a hot running CF card like the HD 6990.
I still have a 8800GTS that is running just as good as it did when it was when it was new. But like anything with electronic components, someday it will die.