Try an external USB keyboard just to confirm the problem exists only on the laptop keyboard. However your system is approaching 8 years old and it may be time to consider replacing it with a much newer much faster laptop.

If the external keyboard works and is an acceptable solution, you are all set.

If not, the price of a replacement keyboard is low enough and it's easy enough to replace that it's not a stretch to simply replace it.

https://www.amazon.com/Dell-Inspiron-3521-Laptop-Keyboard/dp/B00H4FFHYS

Thank you, JOcean, for quick reply. An external keyboard works during the time the internal one does not. Otherwise, I agree with your other conclusion. Will have to think about it. But first want to exhaust all other possibilities to solve the problem.

/hans peter

Restart the computer
Press and hold down the power button until the computer turns off, then release the button. Press the power button again to turn the computer on, and test the keyboard to see if it works. If that does not work, try draining all power from the computer, which helps reset the motherboard.