I have a imac from mid 2011 with 8 GB Memory & 3 TB Hard Drive running Mac OS X 10.10.5. Since yesterday my mac will boot and then shut down. So I went to Mac OS utilities and went to disk and accidentally deleted my 3TB hard drive. Then I wanted to get a fresh copy of Yosemite and it is asking me to choose a disk, there is no disk to choose. Since I accidentally deleted it! PLEASE HELP! I HAVE NO BACKUPS OR ANYTHING!