How to identify what is slowing down the computer

[Prométhée]

Hello
sometimes the computer becomes very slow, and it can be quite easy to identify what the problem is
It may be the memory, which is full, see this article

Add RAM

or an HDD disk, which can be replaced by an SSD if necessary
Or the processor (cpu, see gpu)

Just open the windows task manager, and click on the different tabs

(press the ctrl shift esc keys at the same time )

you should quite easily see, if the memory is full, the hdd, or the processor, by using the different tabs
This can tell if you need more RAM.
or if need to replace an HDD with an SSD etc..

[BeemerBiker]

If your mouse and keyboard are working erratically and your system is suddenly slow

CLICK HERE for general help from Microsoft for speeding up windows

Sometimes increasing ram does not help. If on Wi-Fi then the speed of the network card can cause the problem. A mechanical drive can be the problem.. Windows needs about %10 of disk space free also. If under 5% there can be a real slowdown.

There may be software running in the background causing the problem.  The transfer of data from an internal disk to to an external drive can cause any windows PC to show symptoms such as the Mouse moving erratically.

In your account, open Task Manager (Ctrl + Shift + Esc) and select the Processes tab.  You will see a display similar to Prométhée's image above.

1 - Is either the CPU, RAM, GPU or disk running at a very high percentage,  can you see what process is consuming that resource?

2 - Click the "Startup" tab and see how many items are listed there. Generally, you can disable all. If this make a big difference, then enable one at a time until you find the one or ones causing the problem.

3 - Your account may need to be scanned for "Malicious" software. Generally speaking this is software that is not considered a virus or trojan. It performs unwanted functions such as downloading newer advertisements or reporting what the users is looking to buy and offering alternative suggestions. Typically free games have these apps.
Type MRT in the windows search bar to run the Microsoft Windows Malicious Software Removal Tool. The game or app will not be deleted but hopefully the background process will be uninstalled. This is better than the "step 2" which just disables them.

4 - You can always do a windows update
https://support.microsoft.com/en-us/help/4027667/windows-10-update