The best idea would be to restore from the backup, but if not possible fsck and checking services after rebooting the VM may solve the problem.
After running the fsck from the livecd it may be helpful to check if all the NSX Manager services (vPostgres, RabbitMQ andNSX Manager) have started and NSX Manager has connected to vCenter.
Also checking the LUN that NSX Manager is located in against errors, and checking if NSx Manager running with snapshot could be helpful.
For the procedure of fsck detailed steps
NSX Manager CLI has shutdown command that halts the filesystem before powering off, so if poweroff is needed this command could be used in order to poweroff, similarly reboot command reboots halting the filesystem.
shutdown In Privileged mode, the shutdown command powers off the virtual machine.
reboot Reboots an NSX virtual appliance. Synopsis reboot CLI Mode Privileged