iMac stuck on black screen

My Mac froze on my yesterday, I decided to hard reset so held the power button down but it wouldn't loads after getting stuck on the apple logo, the load bar would go all he way to the top and then turn it self off in a boot loop. I then managed to get into the recovery area by pressing command and R and tried to reinstall the Mac OS but it kept saying there was an error so I erased all to reinstall from using a time machine back up. All seemed to be going well and until the saw a prohibited symbol and now the screen is just stuck on a black screen, can't get back to the recovery area either. Any help would be appreciated?