Mention was made of a another case? I had this problem when I bought an Asus MOBO and 6 core AMD procc', the intended case was too small.
As I had already spent more than I wanted to I went to a local PC repair shop and bought a case (took the MOBO to check!) complete with PSU and optical drive for 30quid. It did not have any sides but that was not a problem. Had it been I would have done same as I did for a grandson's desktop build, fitted it with 4mm acrylic sides and a blue illuminated fan...Looks (and is!) cool.
Dave.