Everything was going perfectly. I made several configurational changes including a change to a static IP address of 192.168.4.253. Note: no drives installed yet. All of a sudden the NAS disappeared from sight.
Were you still able to ping that IP even though the GUI was not available?
I tried to reset it to factory defaults by holding the reset buttion in even though I had no idea if this would work. Several hours later the NAS reappeared at 192.166.0.32
Resetting back to factory defaults will erase all your settings including static IP entries.
1. Why would it disappear for several hours?
Not sure, but good question. We would need to know more info about your network, PC, and other relevant information surrounding these circumstances.
2. How does one reset it to factory default when no GUI access
There's a small hole labeled "reset" between power and ethernet jack. With the unit on, use a paperclip to press and hold down the button for about 12 full seconds. That should reset it back to factory settings (your data should be safe however).
I would also suggest updating it to the latest firmware revision.