How to Clear the PRAM

Symptoms: 

Boot issues, such as slow to start or halted startup.

Causes:  
PRAM is non-volatile memory used by the Apple computers to store configuration information. However, certain changes might remain stagnant in residual memory which can lead to bizarre behavior(s).

Solution: 
Power off your computer. Then power the device on while simultaneously holding down the [command]+[option]+[P]+[R] keys. You should hear the Apple chime before the computer reboots. Continue holding the keys down until you hear the second Apple chime to clear the PRAM.