Before you replace the keyboard, do some work to narrow down whether it is a hardware problem or a driver or Windows problem.  Here are some things to try: Dell keyboard troubleshooting guide[URL] If, after all that, the issue is isolated to the onboard keyboard, then yes, you would need to replace it or use an external USB keyboard. Parts-People has genuine Dell keyboards for your laptop model. Given the age of the system, consider whether you want to spend money on a replacement keyboard, or save up for a newer laptop.
hello  i have a frined laptop here  the left section of the keyboard is not working properly even worst  it type extra letters or incorrect letter  and its not a language issue external keyboard work  should i replace the keyboard ? Thanks   
LaT e6540 KEYBOARD ISSUE