I will describe the way to start syncthing in the background via the Windows Task Scheduler System SCHTASKS. Syncthing will then start with the System and run with the given User-Rights.
Creating the task: Run this CMD line in the syncthing directory or replace %CD% with right path. To run syncthing without login you have to set your USERNAME and PASSWORD.
SCHTASKS /Create /TN Syncthing /TR %CD%\syncthing.exe /SC ONSTART /RU MyDomain\MyLogin /RP MyPassword
Start Synchting task the first time: SCHTASKS /Run /TN Syncthing
Stop Syncthing task, for example to update syncthing: SCHTASKS /End /TN Syncthing