Why reboot the computer
Memory holds data that you and the computer inputs. Occasionally the memory can become full or get some data that may become either corrupt or interferes with an operation that the computer tries to run. When this happens, you may not be able to perform an action that you or the computer needs to do. By rebooting the system, the memory gets refreshed and clears any stuck temporary data in memory. This is the reason rebooting the computer is one of the first steps in troubleshooting a system.
There is two types of rebooting. There is a cold reboot and a warm reboot. For the differences in the two click here. I recommend doing a cold reboot.