I'm new to mac and really know very little about what I'm doing. I was trying to clean install to erase everything, the MacBook was given to my son. tried to erase the partition from the boot option. Apparently this messed it up. I can boot into recovery mode but can't reinstall os x maverick or erase partition. When I try to delete or erase the partition it says can't unmount. This is a older MacBook with maverick not sure of the year. I tried making a bootable usb from my new imac w/yosemite. I can boot up and get the usb drive to boot. The problem when I try to install os x it doesn't see my hardrive. Why will Yosemite usb not see the drive?