Do you know if your memory is in one module of 1 GB, or two modules of 512 MB?
How would your budget react to $34 + shipping for two 1GB modules at
http://www.crucial.com/store/listparts.aspx?model=VAIO VGN-NR120 Series
You computer looks clean enough... but your memory is limited. You need two 1 GB modules of DDR2 PC2-5300 and the address above has a kit of two identical modules.
That may not be the entire fix, but VISTA is a memory hog, and you are using all of what you have.
What I recommend is that you use the Symantec removal tool to remove your Norton software, then reboot and download Avira or Avast antivirus... free for now... and continue to use SuperAntiSpyware free version as well as MalwareBytes free version.
But you may have other problems that we cannot see from here until you have more memory...
Then run a defragmentation,
then run a new scan, one at a time with SuperAntiSpyware, MalwareBytes, then either Avira Antivir or Avast, and Windows Defender.
I think your problem is elsewhere, but we have to weed out the obvious problems first.
In your next post, later tonight or tomorrow, describe in more detail the problems you have been facing, when did they start, with as much descriptive info as possible... but it would be good if we could await your getting the maximum memory... which you can install yourself if you have a small Philips screwdriver...
After two years of use, on 1 GB or memory, it could be anything...
You might want to buy a can of Dust-Off for about $5.00 to $7.00, and clean out the air channel to the fan to get the temperature down as much as possible.
Sony's have a tendency to work great when they are working well, then when thngs slip, the seem to magnify the problems.
With a defragged drive, more memory, better cooling, we should get a better handle on this nice computer.