Hiseeu

These are very low cost cameras for a reason. If you look at the reviews on Amazon you will see they present lots of problems. Best advice is search these forums and buy quality cameras.

How is the cam powered? do the LED's come on when you power the cam up?

if you see the LED's lighting at power up, the cam may have simply got itself another IP address somehow.
check your router's dhcp assignments or run the 'search tool' software provided my the cam's manufacturer.
best practice is to use statically assigned IP addresses (or at least dhcp reservations) for IP cams...

then again, if you don't see the LED's come on at least briefly when you power up the cam, it could just be dead cheap junk...

The led lights turn on when I plug them in, it is powered by a electric plug in with no ethernet port on the wires strictly wirelessly connected to the Nvr system

ok, that's a little more info to work with. check your wireless router or access point's WebUI to see if you can determine the IP address assigned to your camera.
Or use the manufacurer's 'search tool' application that may have come with the cam on a cd, or use Onvif Device Manager to look for the cam on your network.
If you can find the cam on your network, then make sure the NVR is configured to look for the cam at that address. if you can't find the cam on your network,
then it could be the wifi or networking part of the cam has died despite it still powering up as evidenced by the LED's. You might also try plugging it in via an
ethernet cable, if that's an option, then see if you can find it on your network...

looks like the Hiseeu cams use 'CMS' software and 'Device Manager' as search tool, per:
US $29.0 |FAQ Hiseeu IP Camera How to get the serial number-in Surveillance Cameras from Security & Protection on Aliexpress.com | Alibaba Group