The flashing LED only shows that the constant power supply is connected (i.e. the one which keeps the tuning in memory, etc.). There is a separate switched power supply, which only comes on when you turn on the ignition. There will be a fuse in the car's fusebox for the radio, and also a fuse on the back of the radio itself. Check these first. If it's not one of these, it may be to do with the car's ignition switch, i.e where you turn the ignition key. You could use a 12v bulb or voltmeter to check if the power is getting through - it's probably the red wire (yellow for the constant supply) but remember to turn the ignition on to the first click.
Andrew
October 2010