Try different USB ports (at least USB 3.0 or above) or clean Synapse reinstall:

1. Uninstall Synapse
2. Download & run this tool: https://rzr.to/Tf53xj to remove any razer drivers/leftovers
3. Then restart your PC
4. After reboot install Synapse again (as administrator).

I did this but the keyboard still doesn't work. Forgot to say that I'm using a laptop, I also checked the universal serial bus driver and they all is up to date.