Why does my computer fill close to this?

It is a compaq presario nearly 5 years old (so I get that it might be on it's last legs). I added a Radeon 9600 graphics card 3 years ago, and a larger concrete drive under smaller number than a year ago.

The problem: Websites heavy contained by images or video (even sites approaching Youtube) work fine for about 10 minutes, and afterwards it all lags severely for around a minute... afterwards picks up again... then lags... and so on until i acquire annoyed. This happens even if I don't own any other programs running in the conditions.

Also, the problem persists if I am listen to audio (via iTunes or Purevolume, etc.) and doing something else... such as word processing or instant messaging.

I've considered that it may be the mother board. Ideas?

Why does my computer fill close to this?

optimize the start up folder

clean out system tray

verbs temp files

uninstall un used programs

try 3rd party software 'http://www.jdoqocy.com/click-2416861-104...
Yeah this is considered a problem for users that own low ram. You entail to buy a bigger memory stick(ram) which will help tremendously.
Add more push.

http://www.pcpitstop.com for technical check up and counsel regarding your computer.
Depends on what giving of OS you're running, I presume it's Windows XP. You can run msconfig and play around with the startups and services. You can other use more virtual memory, that's basically converting usable HDD space over to virtual RAM space. You might wanna check your observation under errand manager to see how your processes are.