MAC question mark folder

Now, before you freak out as this is quite a common problem let me explain.

About two years ago, I was done with my MAC, and decided to dual boot it with Ubuntu. I ended up deleting my entire mac partition so Ubuntu was the only OS. I ended up running Arch, Puppy Linux etc off of a USB, i then tried a new distro, and messed up on installation, i'm 100% positive I used my dev/sdb for the installation, so anyways I rebooted and got the question mark in the folder. I tried all the commands people were suggesting, and I get no response at all, I'll hold the keys down and nothing will work. I tried holding the option key down, to see if I missed any partitions and I just got a mouse with a grey screen, so I guess everything is gone. Is there anything else I can try? Should I boot any OS from the USB and attempt to just use that in a live environment? Or is my best bet to buy an installation disk or go to the Mac store?