Well you should have bought at least two external hard drives, using one of them as a backup, as hard drives (and especially external ones) all fail eventually.
With external hard drives, however, it's often the SATA-to-USB bridge chip inside the enclosure which fails (a small PCB). Extracting the hard drive from the enclosure and putting it into another enclosure should solve that particular problem. The enclosure you will see has no visible screws. It's held together by concealed clips around the edge. Ingenuity and a bit of leverage is required to crack it open.