Assuming you haven't changed anything on your network except your PC I very much doubt that the NAS is the problem (if you still have your old PC you can test this by reconnecting it to the network).
Does your new PC connect to the network in the same way as the old one (if cabled are you using the same cable)? If you have changed cables, check all the cables at the router are securely plugged in (we have seen where removing one cable plug has also caused another one to become loose and lose connection, I have even seen one case where a cable was pulled out of the plug).
If your new PC connects via Wireless, or has the option to do so, make sure it is:
a) connected to YOUR router and not the one next door
b) if there is both wired and wireless and you have a wired connection make sure that is the default (many PCs with both make wireless the default connection).
Another test is to run something like Netscan (available for both windows and android) to see what is on your network
Netcsan (windows)
https://www.softperfect.com/products/networkscanner/Netscan (android) from Play Store.
For the windows version you will need to know the base IP address of your router. The android version works that out based on its wireless address IP.
I would run Netscan from the PC and an android tablet or phone. I the NAS can be seen by the tablet or phone but not the PC the the PC connection to the network is the problem.