It’s really important that you back up your files as often as possible. In my years of fixing computers I have seen so many hard drives fail and it’s not always possible to recovery the data.
If you want to keep your back up in house, your data must be COPIED to another hard drive, not moved. The external hard drive is just as likely to fail as the hard drive in your computer so your data needs to be on at least two hard drives.
Better still you can upload your data to an online back up site – there are plenty of them to choose from.
Hard drives are not terribly expensive but your data is priceless. Get it backed up!