Hello anyone can help me with my bipolar stepper motor? ;(

hello sir... im having trouble with my bipolar stepper motor. i have already build the two wire circuit for bipolar stepper motor. but the fact is when i tried the to run my motor, it works fine... but after a couple of hours, my motor is not working. im not sure if the transistor is the main problem, or maybe the voltage that i have used... but i used the 5volts of the arduino :(... anyone can help me sir? :( plss.... i really need it on my thesis .... :(

could u please provide the circuit for this???

Firstly you need to have flyback diodes to prevent inductive spikes (this could easily be the cause of the failure). Secondly the transistors mustn't run too hot (this is another possible failure mode - we don't have any information to go on).

Thirdly I would ask for full specs of motor and power supply and whether you run the Arduino off the same supply as the motor (almost always a cause of issues).

Thank you sir... I have used this circuit http://www.arduino.cc/en/Reference/StepperBipolarCircuit . but when i tried to rebuild the circuit, my motor is only vibrating. sir where can i put those diodes? i have a silicon diodes(1N4001) and im using the NPN transistor which is(2N3904). i've already ran it once, and i figured out the whole revolution of my motor is 200 steps = 360 degrees. :(