Stop sign pops up after Apple?

So I was trying to fix my MacBook Air because I forgot the password to it and parent control wouldn't come off. So I tried to restore it to the factor settings by going to utility disk than clicking erase and I clicked on disk 1 thaaaaaan. Started reinstalling Lions and than the page was loading regularly with the apple sign, than all of a sudden this sign that looks like a stop sign pops up the screen and just keeps loading. What do I do!? So worried.