Laptop freezing -- figuring out the issues

Hi all, I have an awesome laptop I bought from my son, a hardcore gamer. So used, but also very beefy and well-cared-for. Lately, however, it has begun to freeze, by which I mean: the screen is not updated, and no keyboard inputs are accepted. So I can't even REISUB; the only cure is the power button.

I like to leave my laptop running overnight for a few reasons -- to get IRC posts while I sleep, to serve *ubuntu ISO torrents, and to run Folding@Home.

Attempting to cure the freezing, I've updated my graphics driver, rolled back to an older kernel, removed my beloved Folding@Home application, turned on the fan overnight, all to no avail. After adding lm-sensors and such, it didn't seem likely to be overheating, but I'd like to be sure about that.

Lately I turned off screen dimming at night and left a konsole window on the desktop running `top`. This morning I found a freeze again, with nothing apparent in the top readout:

So I went looking on the internet and found this super post: Using KSysGuard: System monitor tool for KDE. The first problem was that when I hit Control+Escape, I could not see the System Load tab he mentioned or any way to create a custom tab. However, when I started Ksysguard from the commandline, it matches the screenshots in the blog.

Here is my custom tab:

So tonight I'll leave that on my screen along with konsole running `top` and see if there is any more useful information.