Re: I'm 99.9% sure Hardware Problem
Did you remove the mainboard when you blew out the inside and, if so, did you make sure that when you reseated it, the spacers were properly in place and no part of the mainboard was touching the metal of the case. If it does, this will short out the motherbaord and it will not power on. One way to check is to remove the mainboard completely from the case, place it on a non-conductive surface, such as a wooden tabletop, hook up videocard, monitor, etc, power it on and see if it powers up. Hope this helps.
P.S. Be advised that the case you have appears to me to be a mid-size case and if you decide to go smaller, you are going to introduce airflow and heating issues. With a smaller case, you will need more cooling as there is not as much space to ensure good airflow. The bigger the case, the better the airflow, especially with alot of bulky wires, such as your ribbon cables. If you are deadset on getting a minitower, I would suggest picking up the rounded cables, as they are much less bulky than ribbon cables and don't restrict nearly as much airflow. Be aware of this when picking a case. Just a suggestion. Hope it helps.