my computer model is dell latitude e 5520. last week i up graded my operating system from win 7 to win 8.1, after the upgrade some of the keyboard keys have been functioning even after pressing them. today i changed the OS from win 8.1 to win 7 but still the problem has persisted. my question is how do i fix this problem of some keys such as = and next buttons not functioning?

K squared, November 2015

Your keuboard can be configured in a number of different ways depending on one preferences and locale.

From the controll pannel, open "Regions and languages".
Sellect the "Keyboard and languages" tab.
Click the "Modify keyboard and languages..." button.
In the new window, on the General tab, click the Add button.
You are presented with a list of keyboards families. Click the "+" beside the one that correspond to your situation.
Sellect one that looks correct and click the "Preview..." button. This will display the basic keys layout with no modifiers active.
Once you are satisfied, click the OK buttons to close all windows.

Electro, November 2015

You have probably been eating a cheese roll over the keyboard - small crumbs have got wedged under the key caps. Use a clean brush and a vacuum cleaner to gently remove the debris.

The issue you have is with the keyboard - not with the Operating system as you've discovered.

Good Luck..., November 2015