Depends on what PC you have. Please list your PC specs and details on what type of external drive you want to use. As long as your PC's bios allows you to boot off an external drive such as a USB drive and that drive is big enough then it should technically work if you set it up right. If your problem is that you don't have a hard drive but you do have an external HDD with an enclosure, you can always remove that HDD from the enclosure and install it as an internal HDD if you have a SATA data cable. That is all an external HDD is.