NoMachine v. 7.7.4 ships an up-to-date version of USB drivers which may introduce in some cases some incompatibilities on the system.

If after the reboot of the Windows system to complete the upgrade to NoMachine v. 7.7.4 , it is no longer possible to use one or more USB devices, including sometimes mouse or keyboard, there are some ways for recovering from that state depending if mouse/keyboard are working or not.

First case: keyboard and mouse are working
You are sit in front of the computer.

Uninstall the USB drivers as explained here:
https://kb.nomachine.com/AR12O00955
(ii) How to uninstall USB devices

The most important part is removing nxusbf from UPPERFILTERS in a registry and rebooting Windows.

Second case: keyboard and mouse are not working.
You can connect from remote by NoMachine. Mouse and keyboard will work in the NoMachine session.

Uninstall the USB drivers as explained here:
https://kb.nomachine.com/AR12O00955
(ii) How to uninstall USB devices

The most important part is removing nxusbf from UPPERFILTERS in a registry and rebooting Windows.

Third case: keyboard and mouse are not working.
You are sit in front of computer.

In this case, you can recover by restarting Windows in Safe Mode.

Once system is loaded in safe mode, uninstall USB drivers as described in this article:
https://kb.nomachine.com/AR12O00955
(ii) How to uninstall USB devices

The most important part is removing nxusbf from UPPERFILTERS in a registry and rebooting Windows.