Hey y'all, I've got a strange issue. I purchased a used iMac a couple months ago and it was working fine then. Everything booted fine and stuff. However, I've been having some OS issues and wanted to start fresh with a clean install of High Sierra but this Mac wont boot into recovery mode and it won't boot from an external drive. When it tries, I get the circle with a slash through it. As far as I'm aware, it hasn't had a boot password on it or anything like that and it still boots into the OS just fine, I just cant get it to boot in any other way. It is a old iMac mid 2009 with a core 2 duo. Any suggestions would be great because I'm stuck.