External Hardisk Problem

Hi,
I recently bought a new external hardisk. It’s a 3.5″ Maxtor hardisk. At first I thought it was ok to run. But everytime after I turn it off, Windows is unable to detect it again. I have tried pushing the on and off button again and again but to no success (only sometimes it does). I have scan the hardisk and it gives no problem. I have also tried open up the casing and find no problem with the cable. No loose or anything. I have changed the USB cable but still, couldn’t detect. Could it be my USB port problem? But I doubt so since my thumbdrive can still be detected. Need help here. Thanks!