Need help! Shut computer down while doing a fresh install

Hello all, I purchased a 21.5" iMac today and need some help with it. I usually do a clean install of a new computer and erased the HD as normal, but accidentally shut it down before reinstalling the OS. The problem I'm having is now when I boot up, there is no HD for the computer to boot off of since I erased it, and when I used the Mountain Lion USB drive I created for a clean install, I hold option down on startup and select the drive and it shows a circle with a line through it and powers off. On my Macbook air, which I'm posting off of, I do the same procedure and it goes through the clean install process but doesn't on my iMac. Going to an apple store isn't an option right now since the closest one is several hours away. Can someone offer some advice or options to help?

Also, the main problem I'm having is when trying to do the clean install by holding down option, I see the drive and select it but it does the circle with the line and shuts off instead of doing like it does on my air. Any idea what could be causing this? I finally got internet recovery to start by plugging it in to our network, our wifi wouldn't show up so had to plug it in and hoping it works...

 

Alright I got it figured out everyone! I had to hook my iMac up to a cable connected to our modem because it wouldn't recognize our wifi network for some reason on internet recovery, did the internet recovery and a few hours later it is back working now I then proceeded to go to the app store and mac a bootable USB drive for my iMac, apparently the iMac and MBA/MBP have different drivers so now I have a USB drive for each. Tested the new USB drive I made on the iMac and it works like it should so I'm assuming that was the problem.

Thanks for the suggestions and advice everyone, it helped a lot! I'm about to sell my MBA after getting the iMac because most of the work I do is at a desk and I don't really need the mobility of a laptop, if I do I'll just get a mini iPad or something like that.