Hard drive full or near full can slow the system.  20% left in my opinion will now be considered near full, and slowing the system down.  Burn some of your programs from the hard drive to a dvd disk to free up some space.

 

Spyware will also slow the system so use two spyware programs.

 

If you have less than 1 gb of memory, you need more.  Many like 2 gb that will help

 

Using a Nortons product is a resource hog, and slows the system down.  So if you have one of there products you may wish to change.

 

Make sure you only have your anti virus and firewall boot up at start.  Nothing else is really needed that takes some resources from the installed memory you have.

 

Some of use do a complet clean of the system by reformatting and reinstalling windows to get it back to day one.  Lots of work, but worth it if it has not been done in a long time

What, if any, spyware/malware detection program are you running?

System Idle Process is, um, just that... the amount of CPU in the system being idle.

 

Generally, a bad hard drive is going to start throwing errors. Check the Event Log just in case. I've personally never seen a hard drive just start 'slowing down.' When was the last time the system saw a good defrag? First post you said it was 20% free and it seems now you said it is 40%? Which is it?

 

To rule out/in hardware, try booting into safe mode, which should eliminate a lot of normal processes from loading. If it is still slow in safe mode it is either hardware or malware related most likely.

You did not mention how much ram you have, nor the video card installed.   After a while, the Registry will become corrupted or clogged with many add and removed programs that may mess with the speed of the system.  Many of us do a complete reformat and reinstall of windows to get things back to day one.  If you do this, make sure you back up all the stuff you want to keep or loose it. 

 

Stop Unnecessary Startup programs

Below procedure will provide a faster boot up, and eliminate wasting memory on programs that are not in use at this time, and may help gaming……

http://netsquirrel.com/msconfig / Fair reading on start up programs


 
Start up programs for Windows XP: Click on START, Click on Run, than put in the box MSCONFIG Click OK. Now you are in the System Configuration Utility Program. Click on START UP you see on the top of this Utility Program. Uncheck the programs from here that you do not want to start at boot up, leaving the anti virus and any third party firewall alone. You can always go back into this program to restart them. They will not be uninstalled. Click on APPLY, than it will ask you if you wish to reboot the system. Do so. After it boots up again, you will be presented with another window from the System Configuration Utility Program telling you that you have made an adjustment. If you don't want to see this pop up each time you boot up, put a check mark in the little box in the lower left corner of this announcement.

http://www.sysinfo.org/startuplist.php  Link to a site that can explain what you have starting up, if you do not already know, and which ones you can safely un-check. It’s a long list. Or you can Google Search for what is showing in the Msconfig program, and see what it is...