Take a deep breath, the following is somewhat technical but I hope that you will be able to follow the information.
I suggest that you need to find out whether your PC can see anything else apart from the NAS on your network, not using MS applications such as Windows/File Explorer.
Restart your router, turn off for more than 30 seconds, then turn on again, this will restart any servers etc needed for IP addressing, that may have become corrupted.
Check your ethernet connections on the NAS, Windows machine, router, switches etc, best to remove and re-seat all connections both ends of any cables, wait about 30 seconds after re-seating before starting any testing, there is also the possibility of a faulty cable so maybe change one at a time and test, NAS first.
Use something like Softperfect WiFi Guard here https://www.softperfect.com/products/wifiguard/ use the portable version, it will work with wired as well as wireless networks. This software is designed to keep an eye out on your network by checking at regular intervals and notify you when it finds something it does not know about, it can be very useful.
Run SWG, a search may start automatically, if not start one by clicking on "Scan Now", you may need to select your network card if not asked to do so automatically, the settings can be found under "Settings" (the power switch) "Network Adapter", after the search finishes there should be a number of "hits" and should list all the machines connected to your network.
It should list IP address, MAC address and maybe some other details that SWG found.
It will pop a notice that it does not know some devices, at this stage ignore the notice.
Softperfect ©️ screen shot
If your NAS is not found with SWG, check the NAS setup.
Do you know the NAS IP address?
How are you managing the NAS setup if you cannot connect?
Try pinging another IP address that was found with SWG and see if that returns a success result (see below)
A good IP address to try is your router, the default IP address is most likely what you are using, its IP address is usually listed somewhere on the router itself or can be found with an Internet search, preferably using something like DuckDuckGo https://duckduckgo.com/ or Startpage https://www.startpage.com/ .
To ping an address with Windows start a command window using the "Windows" key(https://en.wikipedia.org/wiki/Windows_key the one with the Windows flag) and "R" (press together), then type in cmd and then click "OK", if no Windows key then click "Start" or whatever you use, bottom left on the Windows taskbar, then click "Run" then type "cmd" in the space provided, then click "OK".
Once the command window is open, type "ping" a "space" and the IP address of of your router, for example "ping 192.168.1.100" replace 192.168.1.100 with the IP address of your router found using SWG or internet search.
The results of the success ping I used "ping 192.168.1.250" with the result listed below the typed line and should indicate whether the Windows machine can see the IP address used at a lower level than Windows/ File Explorer.
I changed the IP address to "192.168.1.200" in the failed example to an IP address that has no machine allocated, so it failed, great.
Examples, don't worry about what it all means, just that you get reply that says something like in the first example.
Microsoft ©️ screen shot
Success, machine is alive and can be seen from the Windows machine, move on to "HERE" below.
Microsoft ©️ screen shot
Fail, machine cannot be found, if you searched for the NAS, check NAS settings.
When you have checked the NAS settings re-run SWG to check connection to the NAS is up.
Check connection to the NAS with Windows/File Explorer, if not successful then the problem is most likely with the network setup in Windows and will take a deeper search to find a resolution.
Perhaps try some of the other suggestions again now if you can see the NAS is up with a ping.
Do you use DHCP or static IP addressing?
Apologies if this is too much.
Makes some sense.
Hope it helps.