You paid someone to build it for you? Either send it back or get the necessary hardware and fix it yourself. But just from your description I couldn't go about telling you what to do. Obviously a fan shouldn't be hanging loose like that.
I bought a pc and it arrived today. It has Cooler Master HAF case. It has a cooling system, that I don't know how to use. And everything inside the pc looks to be plugged in and ready except for that. And there is a fan looking out the back that is loose and I can't place it in. It has the rubber screws and one is In but the others are tight. I have seem tutorials on YouTube but none of them show how to fix it when they have already been installed. I can't put them in as they are short. This is my first time dealing with an actual pc and would appreciate your help. Thank you.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic