Well several things are making it hot...with just one exhaust fan, the air that needs to get in so some can get out is likely coming in thru your rear case grille and bringing your hot PSU and GFX card exhaust along with it.
Again, with the scant information being provided, its hard to offer any productive recommendation other than adding the missing intake fan. But with just 2 fan mounts in total, you don't have many options with that case.