My arduino robot not working well

i dont know why i upload the example code for motor turn and the robot not turnning well just vibrate. n also effect to line follower example code. PLS HELP ME.

There could be many reasons,

Please put your code in its own window as seen in other posts. This can be done by placing     [code]  and [/code]  around the code or use the </> icon. This makes it easier for others to read.

How to use this forum

Also draw a circuit, photograph it and post it.