Clean install of mountain lion..

Two weeks ago i try to clean install mountain lion on my mac book pro 15" (2012).. But unfortunately the installation failed..so now i try to re-do the clean install.but it keeps on saying that ii cannot install it..then when i restart my mac and hold down alt(option) ,,the only thing that will appear is the bootable mountain lion flash drive..unlike like time that when i restart then press alt(option) ,,it will show macintosh hd , recovery hd and the bootable flash drive..what do you yhink happened to my mac???can someone please help me