I, too, had a similar problem (with nvidia-glx-195 on a Karmic box), and the problem cleared up after I installed linux-headers-generic-pae. I'm now successfully running 2.6.31-16-generic-pae and nvidia-glx-195 and seeing all 4 GB of RAM in my system.
I, too, had a similar problem (with nvidia-glx-195 on a Karmic box), and the problem cleared up after I installed linux-headers- generic- pae. I'm now successfully running 2.6.31- 16-generic- pae and nvidia-glx-195 and seeing all 4 GB of RAM in my system.