PS3 System Power
The DualShock 3 controller derives its power from the PS3 gaming console. Not only is it used to charge the controller using a USB cable, it can allow you to control the game when it isn't in wireless mode. The controller cannot be synced to the gaming console if the system is off. If your gaming console isn't turning on, check that the AC power cord is inserted tightly into an electrical outlet. If the gaming system has been dropped into water or isn't turning on, you may have to contact Sony support.
Charging
A PS3 controller uses an internal lithium-ion battery. It won't sync if the battery is dead. The controller's battery loses charge even when it's not in use. Connect the controller to your PS3 using the USB cable and charge it before syncing it to your gaming console. Once connected to the system, the port indicators on the controller will begin to flash slowly when charging begins, and stop completely when the battery is fully charged. Keep in mind that the controller cannot be used while charging. Additionally, it cannot be charged when the system is off.
Solution
Push the reset button on the back of your controller to reset it. Although resetting reboots the controller's hardware and restores the default factory settings, it's a final troubleshooting step capable of solving syncing problems. Resetting your controller may also solve other problems related to slow response times and erratic performances. Resetting your controller clears the sync information and the number assigned to it, so you have to resync the device to your gaming console in order to use it.
Re-Syncing
Turn on your gaming console and wait for the LED light to turn green before syncing the controller. Connect your controller to your computer using the USB cable. Press the PS button and wait for the four port indicators on the controller to begin to flash. When the light turns solid red on one of the four indicators, that number is automatically assigned to the controller. PS3 can connect up to seven controllers at a time. Keep in mind that pairing and assigning controller numbers can only be done when the system is turned on.