does factory reset on a pc delete external hard drive files?

Welcome to the community, XENURINE!

The factory reset shouldn't affect the data stored on your external hard drive. However, it would erase data stored on your computer, so make sure you have a backup of the files from your internal drive elsewhere!

Best of luck! :)
SuperSoph_WD
 
Would also add that if all your files are stored only on one external hard drive you should really have them stored on two for full protection against data loss in case one of them fails. External hard drives are more prone to failure compared to internal ones so you need at least two in case that happens.