The mobo just slides right out from under the hard drive cage once the cables are removed.
In addition to the Torx wrench and 4 silver screws on the door, there are actually 16 screws along the bottom of the door. Combined with the 4 screws included with the Seagate drive, HP included enough screws for 5 drives.
This is the 2GB stick of RAM that came with the NAS (Samsung 2GB ECC DDR3 PC3-10600). This is later replaced with a Kingston 2x4GB unbuffered ECC DDR3 PC3-10600 kit.
The 8GB kit of RAM is now installed. You can clearly see the PCI-E slots on the left.
This is the HDD that came with the NAS. It's a 250GB Seagate 7200rpm SATA II drive (model ST3250318AS).
HP included a Torx wrench and 4 screws on the door. The screws that held the Seagate HDD in the mount had Torx heads. It's camouflaged really well.
Here's what it looks like all put together with 4 hard drives installed.
There's an internal USB port on the mobo. FreeNAS is designed to run on a thumb drive, so this is a logical place to put it to get it out of the way.
The N40L (left) is definitely bigger than the N4100Pro (right). Most of the height difference is because the N40L has the 5.25" bay on top. The cable coming out of the N40L is a USB keyboard. This thing has lots of USB ports (4 front, 2 rear, 1 internal).
Here, you can see the lights. The blue HP logo is the main light on the unit. There are a few green signal lights on the top right. Although the HP logo looks super bright here, it's really not that bad.