My first impression was to see what Task Manager looked like to see if CPU usage was at/near 100%. But didn't see that in your screenshot, but saw something interesting about memory usage.
According to the screenshots, at the time, you were using almost all of your 512MB. As you get near that number, the computer automatically starts using a section of the hard drive as RAM. A trip to the hard drive is a thousand times slower than a trip to RAM (in CPU years). Also, it looks like you were probably well above the 512MB mark as some items were using 150MB by themselves.
It's normal for the computer to lean on the hard drive when memory gets full, it keeps the computer from crashing (as often). Some of the big offenders look like:
* Internet Explorer
* SpySweeper
* ehrec.exe...a Windows Media Center file
* mim.exe...MusicMatch
There's a few big hogs, and oddly, a high number of medium size hogs. There's a few ways to go about it:
* Throw hardware at it..upgrade to 1GB of memory, if it turns out that it is a memory problem
* Search for the errant programs..takes a while to figure out what each one is doing...Googling each and every one on the list to see what it does. Uninstalling/Reinstalling certain software. Even then, this is just a guess as to what the problem is.
* Backup your personal data and reinstall Windows...the "nuke it from orbit" approach (just to be sure).