Nvidia drivers slow down the comp.

Hello.

I'm French, so excuse my bad English and it is my first post on these forum so i don't know if i'm in the right forum. I have already seeked for this issue but i didn't find anything.
I've got Nvidia 6800 GT graphic card and a P4 2800Ghz proc under debian (with a compiled kernel).
Now, i'm running with vesa standard driver, but when I use Nvidia non free drivers or nvidia free drivers, my pc incredibly slow down and i can't do anything with comp. Furthermore, graphic bugs appear (vertical line popping) and applications who need just a bit of graphic skill (as web browsers) make the comp crash.
I'm wondering if the problem comes from the drivers or from the material which has been shocked many times...
Thanks for your help.

LaicepS

I believe you are having the same problem as mine , most probably it's related to the kernel configuration , i used the standard debian 4.0 one and no problem ! by the way how did you install the driver ?

Regards.

To install the free drivers I followed a howto found on internet, and for non free, I executed the package from the offical site.