Push the power button (which you should have incorporated into your design already) and see if your computer works. If so, good job, you just built a...
Today my family cleaned out our basement and found some old cardboard boxes. My family was going to throw them away, but I decided to use for something. I had an old computer with a lame processor and not much ram, so i decided to do something cool with it.
2. Cardboard box with slightly larger dimensions than your computer's mother board.
3. Duct tape
4. Scissors or knife
5. Lots of time
6. That's it...
Step 2: First box
Place your motherboard into a box and install all the ram, graphics cards, and hard drives. Cut out areas for the plugs and ports. I encased the hard drive, minus the top and plug sides, in cardboard to insulate the metal from the rest of the mother board. I didn't think of making an instructable until i had already done some of this stuff so sorry if you don't understand the beginning assembly. I suggest testing your setup as of now to make sure it's not messed up. I also suggest testing this thoroughly throughout this setup.
Step 3: Revision
I just figured out that my hard drive was overheating, causing my computer to restart randomly. Make sure you keep your hard drive in an open place. I'm open to suggestions on better ways to incorporate the hard drive, so please comment.
Step 4: Next...
Cut holes in the box to add a second box on top. I cut two holes for fans, one for the processor's and one for another.
Step 5: Second Level
Add drives and PSU on top in a way that fits together, kind of like a puzzle.
Step 6: Structure
I added a layer of duct tape on the front to help hold it together.
Step 7: Finalize
Put a final layer of cardboard on top of the box to seal it off. I purposely made my final layer in a funky design