My external hdd 3,5" 1,5T from Maxtor is working without any problems under Win7, but it's not working under Win8.1. The system detects an unknown device and that's all. It just won't mount. Even my Mac and Ubuntu can't mount the hdd.
First check your USB port for functionality with another device to make sure thats not the issue. Likely its a driver issue. Uninstall your drivers and reinstall them. Maxtor was accuired by Seagate a while back so thats where you'll have to get your support for this device.