TV tools is a software that is supposed to manage and control nVidia cards TV out.
If you have made the mistake of installing this software without reading the documentation first. Your screen may go blank and there is nothing you can see. even after a restart.
The solution is to press Ctrl+F2 right after the screen goes blank. But if you restarted your system, this is less likely to work.
What you can do is to restart and hold f8 before windows starts. then select “Enable VGA mode”.
You will be able to see the desktop at low resolution. remember not to increase the resolution yet.
Open TV tools and then normally increase the resolution to that you usually use (1024*768 or else).
The screen will go blank again. Now press Ctrl+F2. your display will be restored.