There might be a hint in the logfile in C:/Users/[yourid]/AppData/LocalLow/MeshedVR/VaM/output_log.txt
Try starting SteamVR 1st. Make sure everything is working and controllers are on. Then launch VaM.exe. You can also force to use SteamVR by launching VaM (Open VR).bat but that really should not be necessary.