Why is my Windows PC slow?

duno

I do think computers run the same speed most of the time. So "running slow" usually means one or more resources are at or near maximum. When you notice "slowness" how to determine which resource(s) are being taxed?

Use Task Manager to determine why. Task Manager is a misnomer as Windows does not have the concept of Task as do other operating systems.

Task Manager can be invoked in several ways. CTRL-ALT-DEL brings up the Task Manager in cases where other attempts may fail due to resource exhaustion. After CTRL-ALT-DEL (press and hold the CTRL, ALT and DEL keys at the same time) you should get a screen with:

Lock

Switch User

Sign Out

Change Password

Task Manager

Cancel

Task Manager can also be invoked with the Search window or right click on the task bar. Once invoked you should see a new window similar to:

The first tab shows the processes on the system and their percentage of maximum. In this case 100% of the CPU is being used. Other resources are Memory, Disk and Network. It is important to note memory and CPU can be 100% used but not taken. The processes that have multiple windows open or instances will have an arrow to expand that selection.

On the Performance tab you will see the window similar to:

at the bottom is a link Open Resource Monitor. Using this link brings up another window:

By having both Task Manager and Resource Monitor open you can investigate the cause of your "slowness". Click on any column to sort in that column.

To return to the point made before of CPU and Memory using or taking 100% of the available.

System cache will use unused memory for filesystem and other caches. Background processes will use any unused CPU cycles. The scheduler monitors these two resources with an attempt to maximize the use of the limited resources.

Once you have determined the processes utilizing the constrained resource you can determine the course of action (if any) you can take to restore the resource usage level to "normal".

In the process of using these tools to determine resource utilization, I hope you get the User Access Control (UAC) popup window to supply an Administrator password.