It sounds to me like you've lost the original packaging for the case and the components.
Usually there is branding found around the case either on the back, front, side panel or at the top most of your chassis to help distinguish it from the rest of the brands out there in the market. From there it's either as simple as finding the chassis in the manufacturer's site, performing a google image search or asking around forums with a picture of your chassis + internals to help the community identify the chassis.
Is it possible to pass on a picture of your system and perhaps a link from where you've purchased it from? Your question is two folded actually since you'll need to know what sort of fans are compatible with your case and the best...