|Just as the message says: One of the devices connected to USB draw more current than allowed (0.5 Amps).|
1. Disconnect all USB devices, including cables. Start computer. Connect one by one to find out which one draws too much current, or maybe is malfunctioning.
2. If you still have that message with all USB devices and USB cables disconnected it means you have an USB port short-circuited. I've seen this. Look at the USB ports with computer shut down and unplugged to see which USB port has been abused. Try to straighten out the connector so that no short circuit occurs. Would be wise to avoid using that USB port after this, because once bent, it will never be as hard (tough, resilient) as when it was new.