Nothing showing on monitor after not using 2-monitor cmputer fr awhile

A couple of years ago I bought a used corporate desktop PC with Windows 7 and used it for a while. Then I bought a new laptop and I haven't used the desktop since. Now I need to get a couple of programs off the desktop. But when I turn it on nothing shows on the monitor. The computer sounds like it's booting up okay.

I am using the very same monitor that I used before when it was working. (I am typing on this monitor right now (with the newer computer)). This desktop has a large port for a monitor that you connect a splitter connector to and then connect the monitor to one of the two smaller jacks coming out of the splitter connector. As I recall. when I first bought the computer I connected my monitor to a monitor port on the computer which fit the monitor's cable and it didn't work. I contacted the seller who told me to connect it to one of the splits and it worked.

But for some reason now it's not working. It could be something simple. It may have something to do with the 2-monitor configuration of which I know little.

So my question is how can I proceed toward seeing what's going on on this Windows 7 desktop computer enough to retrieve several Visual Basic programs?

Yes.