From Task Manager, find process “googledrivesync.exe”, then click End Task
Open folder C:\Users\Administrator\AppData\Local\Google\Drive\user_default
Open file sync_log.log to figure out what really happened. Just for knowing more details. The solution is just restart the googledrivesync.exe
Delete file : pid, lockfile, run_dir → if these files still exists, it serves as mutex which inhibit googledrivesync to start.
Start googledrivesync.exe → hopefully back to normal