why-- after searching for a while on my desktop computer?

Boot your computer from a power-down situation.

Bring up task manager and look at the running processes. Write down the number of processes.

Perhaps spend a few minutes researching the ones you do not know. You may want to un-install or disable some of them from startup.

After a while - when the PC starts slowing down, check the process under TaskManager again. Did any new ones come up and are taking a lot of CPU or memory? Investigate these and perhaps kill them.

It could also be your browser, like if you are using Chrome...try something else like Firefox and see if it happens. Other things to try would be making sure your HDD isn't going bad....

If you're opening many tabs in chrome, you are probably hitting the RAM limit, since that machine only has 4GB RAM and some of it has to go to the iGPU (128MB-1GB), and Chrome can easily top 2 GB...The OS needs 1-2GB...Now you see the problem? Because you have paging on, it won't tell you that you are running out of memory, but paged memory IS SLOW.

Possible causes

1 -Overheating. Check the fans and take off any dust off the vents. There are also a few free apps out there that check for CPU, GPU temperatures (Search for SpeedFan in Google) . Take it to a PC repair shop if it's running hot.

2- A failing RAM module. Check your installed RAM using Control Panel\System and Security\System.

It means you are using a stone age Computer ❗

Best luck

If you are there i will help.. ok good luck.. let fix it ....uninstall all browsers download ccleaner and clean up your files and your reg keys... reinstall your browsers.. If you pc is old your av will slow down your pc that will be later... now we will tune up your your pc.. https://www.youtube.com/watch?v=KqpX_rb5VNk . Let me know it it works.. IF IT'S NOW AS FAST AS YOU LIKE UNINSTALL YOUR AV AND INSTALL PANDA FREE AV AND USE WINDOWS FIREWALL......

Clean the dust off of the heat sync.