Hey, I'm new to this forum and, don't know much about Mac. I have a Macbook Pro mid 2012 edition. I recently Installed a used SSD (Samsung Evo 850 250gb) in place of my HD, and took out the optical drive and placed my HD there instead. I have a USB to boot High Sierra on the new SSD, which i'm planing on using to boot my Mac. The problem is, when I go into disk utility I can't erase nor partition the disk on "Mac Os Journaled". I get "Could not mount disk1s2 after erase", and "Operation Failed". I can only partition the SSD on "ExFAT", but I can't load the operating system on ExFAT format. I've tried force erasing the disk via terminal but that too gives me error, and says "Could not mount disk1s2 after erase". I've also tried going into recovery mode with "Command + R" and trying to erase/format the SSD from there but it gives me the same error. Any help will be highly appreciated!! THANK YOU!