A common cause of the
tftp server not seeing the 'probes' at startup of an NVR or camera is the Windows firewall blocking the inbound access to the PC.
To check and fix this for Win7 - though this has not always worked on Win10, not sure on Win8 - use:
Shut down the tftp server.
Start | Control panel | Windows firewall | Advanced settings | Inbound rules
and delete all rules associated with tftpserv.exe
Start the tftp server, and when Windows announces that it has 'blocked some ...' ensure that both Public and Private networks are ticked, and click 'Allow'.