Device drawing too much power...?

Am trying to charge my original iPhone and both the wall charger as well as computer (mac) do not seem to allow it to charge. When I plug into my computer, I get an error message that says:

+Because a USB device was drawing too much power from your computer, one or more of your devices have been disabled. To prevent damaging your computer, the USB device drawing too much power may have also been disabled. When you disconnect the device drawing too much power, your other USB devices will be enabled again.+

When I press the power button on the phone, I get the low battery icon on the screen (red bar showing it needs to be plugged into a power source).

Not sure what is happening or what to do... Can anyone help?

Thanks so much in advance.