OK, let me see if I have this correct.
Your network consista of;
1) Arris TM722G cable modem,
2) Netgear N600 wireless router. Standard IP 192.168.1.1 with 100Base-T ethernet ports,
3) TEG-424WS Part managed Switch. Basic 100Base-T ethernet ports with 4 gigabit up/down link ports. Standard IP 192.168.0.1,
4) D-Link DGS-1100-08P an 8 port gigabit smart Switch with PoE capabilities. Standard IP 10.90.90.90,
5) D-Link DNS-320L NAS.
At some stage there was a power failure which forced all units to be restarted and because of this you have lost contact with the NAS. It also appears that you do not have control of those devices and so can not check their settings.
I would say that the main problem is a network setup problem and, unless the power failure has damaged the NAS, has nothing to do with the NAS itself.
If you were able to do the setup checks we would be able to talk you through what to do but it appears that you need to involve the IT support people now. Sorry.