Sometimes, Macs tend to have issues that can't be resolved by normal troubleshooting. You don't think its a hardware issue, and you really don't want to have to make an appointment to visit an Apple Retail Store, only for them to tell you that your thoughts were correct! Before determining something is a hardware issue, and once you've done standard troubleshooting, you could try doing a System Management Controller Reset.

 Indicators you may need to reset the SMC:

 Fans: The Fans may be running very fast and very loud, even though the computer is not currently under heavy stress levels, and is being properly ventilated.

 Lights: This includes Keyboard Backlights malfunctioning, Status Indicator Lights misbehaving, Battery Indicator Lights not working properly, and Display Backlights (if your Mac has this feature) not responding to changes in Ambient Light.

Power Issues: Your computer may not respond when the power button is pressed, a MacBook may not respond properly when you open / close the lid, the computer may go to sleep or shut down without warning, the battery may not be charging properly when on AC power, or the MagSafe power adaptor LED isn't indicating the proper activity.

 System Performance: The computer may be running extremely slow even though you're not currently putting it under heavy load and its not experiencing high CPU utilization, Application Icons may bounce in the Dock for an extended amount of time when launched, Applications may cease to function properly and even stop responding after being opened.

Video: Computers that support Target Display Mode do not switch into, or out of, Target Display Mode as expected, or computers that support Target Display Mode unexpectedly switch into or out of Target Display Mode.

 Port illumination (Mac Pro Late 2013): Illumination around the I/O Ports does not activate when you move the machine.

 So, how do you reset this SMC, you may be asking? Read on to find out how to do it for your particular model!

 Mac Notebooks w/ Non-Removable Battery:

 This includes: MacBook Pro (Early 2009) and later, all MacBook Air models, MacBook (Late 2009), and MacBook Retina (12-inch, Early 2015)

 1) Shut down the computer if it is not already shut off

2) Plug the charger into your computer, as well as a power source

3) On the built-in keyboard, press Shift-Control-Option and Power at the same time; Release all 4 simultaneously

4) Press the Power Button to turn on the computer