At that age the heatsink compound dries and will crack. You can see what happens in the video to follow it can slow down. Errors can occur all over the map as well.
If this was mine, I'd pull the heat sinks to wipe off the old compound and apply the new compound as I clean the machine up.
Video -> https://www.youtube.com/watch?v=y39D4529FM4 the first 35 seconds shows the typical slow down.
As this is usually met with folk replying "it's not heat" or they trot out CPU heat software measurements, I nod and carry on. It's their machine.
Bob
I installed a "used" 300 watt power supply in my HP Pavilion 743g desktop. After approximately 8 years the 200 watt power supply burned out and I purchased the computer used. Since installing the replacement power supply, I now have "no" Windows XP start-up or shutdown sounds although the sound for everything else still works. There is also a long (12 minute) boot-up time when I turn the computer on and programs are opening slowly. It is a Pentium 4 with 1gb memory and a 2.4 GHz processor. When I go to control panel sounds for Windows exit and start up, I get a "Windows cannot find %SystemRoot%/media/Windows XP Shutdown.wav. Do you want to use the file for this event anyway? Yes or No" message with neither choice fixing the sound issue. Do you have any suggestions for the slow boot-up and opening of programs. I can live with the sound issue if I have to. THANKS!!!

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