Is there any alternative to UltraMon to be able to quickly turn a screen on and off.
I'm using multiple monitors and but have a piece of software with features that doesn't work when two monitors are enabled.
Windows Vista, nvidia, using the windows control panel currently.
I've found that the easiest way to switch on/off the external monitor is to use Windows' own control panel. I have a workstation with two monitors, but one of them doubles as an external monitor for my laptop. When I need it for my laptop, I just flip it off using the control panel (right-click on the desktop and select "properties").
You could use any automation software to manipulate the control panel. I like AutoIT myself
BTW. Is this really a programming question? If it is then I'd advice to fix the software rather than look for hacky workarounds. Multiple and/or large monitors are becoming quite popular these days.