Wireless Internet connection and shutting down

I have a Dell Inspiron N5110 Laptop and the wireless internet no longer works.  It used to work wirelessly, but the past year I have been unable to connect to the wireless network and retain the connection.  I have been told by an IT technician that the laptop is too old and should be replaced.  It is only 5 years old.  Could you please tell me know how I can connect to the wireless internet and whether I should look at replacing my laptop entirely.  There is another computer in the household which doesn't have a problem with our wireless connection.  My laptop also sometimes randomly shuts down.