Look over the power cable going from the wall outlet to the back of the Seagate hard drive. Make sure that there aren't any breaks or tears in the electrical wiring. If there are breaks, replace the power cord.
Look over the power cable and make sure that it is plugged into the wall outlet in your home as well as plugged into the back of the hard drive.
Plug the power cable directly into the wall outlet or into a surge protector. Do not plug the power cable into an extension cord.
Disconnect all of the USB devices that are plugged into your computer's USB ports except for your mouse and your keyboard. Disconnect the Seagate external hard drive from your computer.
Unplug the power cable from the back of the Seagate external hard drive and restart your computer. Wait until your computer has fully booted and then plug the power cable back into the hard drive.
Look over the USB data cable to make sure that there are breaks or tears in the cable. Look over the ends of the cable where they meet the computer and the hard drive. Make sure the pins are straight.
Replace the cable if needed.
Plug the data cable into the back of the hard drive. Plug the data cable into your computer.