Arduino makes noise and LED blinking

Hi,

I was working on my arduino project (with a motor shield L293D, 4 DC motors and a bluetooth chipset).
Everything was fine and then, all of a sudden, when i connected my arduino to my PC, it started to make a noise while blinking faster and faster and i can't even load a new sketch into it. It says the arduino is not even connected.
But when i connect it to the battery, it runs the old sketch well, without this blinking bug.

Did some of you already experience that and would be able to help me?

Does the problem still occur if you plug in the Arduino board with nothing else connected to it?

Thanks for you're reply, it's does not occur when there's only the arduino, thank you. It seems the usb wasn't giving enough power

Max current normally on USB is 500 mA.

Certainly not recommended for the types of load you are using.
Running things like that have on occasion taken out boards for people.
Sometimes it is worth a little extra time to read up a little more on a product before throwing caution to the wind.