Graphic Card problem

In my system is an agp nvidia 6600 card from xfx. Lately I've noticed everytime I'm watching flash based video on websites like Sky sports and other sites my cards starts making noises or the pc throws a bsod and just reboots.

Last year I used some program [riva i think] and put the fan speed 30% lower to get the noise issue handled as I wasn't gaming. Do you think that might be the reason?

Possibly, first thing i would suggest doing is removing it and making sure the fan / heatsink is free from dust.