there is a same question in:
SetCursorPos and GetCursorPos not working at login screen?
the answer as resovled was
Alternative solution: It is possible (but very tricky) to use mouse_event (which does work at login screen) instead of SetCursorPos. I don't have time to post code now, but if asked I may update this answer...
so, does anybody know how to use mouse_event to move mouse cursor in windows login screen? thanks!