Hi zubair_riaz,

Did you press and hold the shift key for a longer time? If yes, you may go to start --> control panel --> Go to "ease of access options" make sure that all the accessibility options are all unchecked. When you hold the shift key down too long, one of "sticky keys", "filter keys" and "toggle keys" turns on and you will see an icon of a stopwatch in the bottom right of your system tray (where you clock is). If you see this, you can left click on it and turn it off.

Another step you may try is to  the keyboard language settings. Make sure that keyboard layout is set to US and not US - International. For more information on this, you may refer to link: http://bit.ly/13tSSQ9 

You may also try the steps follow:

Click Start > Control Panel > Region and Language and in this window navigate to Keyboard and Languages tab and click ‘Change Keyboard’ button. There will be several languages listed under ‘Installed Services’. Please select the language you do not use or not required and then click Remove. Likewise remove all the unwanted languages and check the keys functionality.

I also request you check keyboard functionality in Command prompt. For that restart the system and at the Dell logo tap the F8 key every two seconds. In the ‘Advanced Boot Option’ window using down or up arrow key highlight ‘Repair your Computer’ and hit enter. Select the keyboard layout and click on ‘Next’. On the ‘System recovery Option’ menu click on ‘Command prompt’ to open it. Use your keyboard in this window to check if it works fine. 

Once done, check if the issue persists and share the findings.