VGA is an analog signal, so for the monitor to generate the proper image, it needs to apply that signal to the proper number of vertical and horizontal scans per second. Unfortunately, not all monitors support all scan rates. You will get that message when you're trying to drive the monitor at a scan rate it's incapable of.
Are you sure you have the proper resolution for the monitor? Search online for the native resolution of that particular model Dell monitor. Then set your Windows resolution to that resolution.
If it still doesn't work after you're at the native resolution, you're going to have to try tweaking the refresh rate (which is the vertical scan rate)
https://www.lifewire.com/how-to-change-monitor-refresh-rate-setting-in-windows-2626207
If that doesn't work, you can try searching for and installing drivers for that particular monitor. These aren't really drivers, but they're a list of scan rates the monitor supports so Windows can offer the proper supported resolutions and refresh rates.
If it still doesn't work, then the monitor is probably broken. It's not unheard of for the scan or sync electronics in older monitors to go bad.