6 Volt Futaba Servo controlled by a 5V Arduino

Have you tried going through an Arduino servo example/tutorial? The linked example shows one thing you are missing: a call to refresh()

refresh() You must call this at least once every 50ms to keep the servos updated. You can call it as often as you like, it won't fire more than once every 20ms. When it does fire, it will take from .5 to 2.5 milliseconds to complete, but won't disable interrupts.

Edit: as TheTerribleSwiftTomato mentioned, you are not checking the value of movemotor but setting it. Because of this, the first if statement should always be true as any non-zero value will evaluate to true. You can avoid these assignment condition errors by adopting the Yoda condition style. It looks a bit funny, but helps the compiler catch errors for you.

Your servo may behave erratically, and you may find that this only happens when the Arduino is plugged into certain USB ports. This is because the servo draws quite a lot of power, especially as the motor is starting up, and this sudden high demand can be enough to drop the voltage on the Arduino board, so that it resets itself.

If this happens, then you can usually cure it by adding a high value capacitor (470μF or greater) between GND and 5V on the breadboard

http://learn.adafruit.com/adafruit-arduino-lesson-14-servo-motors/if-the-servo-misbehaves

As others have commented, if your servo requires more current than the Arduino (or your USB port) can supply, you should provide a separate power connection for the servo.

Your USB port may be limited to 100mA or to 500mA, the Arduino may be able to provide slightly more current at 5V if it is connected to a power source through the barrel-jack connector. It depends on the specifications of the 5V regulator on your particular Arduino (or clone).

If you power the Arduino from a regulated 5V supply, you can draw higher currents from the V_IN socket.

I note that some retailers of your servo suggest it be used with a motor controller board.