external hard drive problem

i have a 500 gb comstar ext hard drive on which i store movies. I can access and play them on my pc, but after a while it appears the connection starts to faila s the blue ligth on the ext hard drive starsts to flicker. This is more exaggerated if i try transferring an entire file to my pc...the connection loss occurs much more quickly. when i access device manager on my contrl panel.the storage drive is healthy

-any ideas as to cause
-do i slowwly one at a time move my mvies and then reformat