I'd change the router ip address back to what it was and alter the NAS ip address connect the NAS up to a monitor and keyboard for this and note the ip address, ensure none of the other pc's are using that address at the time.
Once it's back in the closet on its own you'll need to Telnet into the NAS box from your other pc to change any settings and to reboot or shut down.
Assuming your other pc is running Windows XP go "start" then "run" then type "telnet ***.***.***.***" * been the ip address of the NAS, you should then see the console, log in as normal and perform the functions you need, when shutting down follow the onscreen directions but then you'll have to manually go and turn off the power to the unit once you get the "telnet disconnected" message
If you do a straight forward power off NASlite runs a disk checking procedure before remounting the drives and it can take a while, especially with 800Gb of HDD
Good Luck and any problems post back