To resurrect an old thread, which was the first I found when looking for the answer, I made the following to deactivate the saver on Win8.1. Maybe useful for others... #include <File.au3>
func KillScreenSaver()
local $szDrive, $szDir, $szFName, $szExt
$sspath=RegRead("HKCU\Control Panel\Desktop","SCRNSAVE.EXE")
if @error<>0 then return 0
_PathSplit($sspath, $szDrive, $szDir, $szFName, $szExt )
$SCRproc=$szFName & $szExt
if ProcessExists($SCRproc) Then
processclose($SCRproc)
ProcessWaitClose($SCRproc,1)
EndIf
EndFunc