If the power and data lights are both blinking and the device is 2G+ then the USB button on the front of the device was most likely pressed when the unit was powered on. This will cause the unit to not work.

Power-cycle the unit to get it back to a working state. If the USB button was the problem then the unit will boot normally.

If the unit does not boot normally at this point, the problem is most likely related to the power supply.