You can use the Registry Editor [
Regedit.exe from command line] and find and edit the following key:
If your screen saver is currently enabled the value will be
1, change it to
0 to disable.
Before you make changes to a registry key or subkey, Microsoft recommends that you export, or make a backup copy, of the key or subkey. You can save the backup copy to a location you specify, such as a folder on your hard disk or a removable storage device. If you make changes that you want to undo, you can import the backup copy.
More info here