Replying to External hard drive power problems...

hello everyone. im hoping someone on here can help me. so i just got an wd external hard drive taht connects to my comp through the usb...no external power source is needed...its awesome. i needed to reformat my hard drive and it allowed me to save everything i need like music and pics...and it has been working great except for that sometimes i get a little bubble that says my external hard drive has exceeded its power and is basically using too much power and it disconnects it. then i just reconnect it and its not problem, unless im editing videos or listening to music, and it is starting to get really annoying. does anyone know why this is happening or what i can do to stop it? thank you so much for your time and help!