On the back of the monitor is the Model number. Go to Product Support  tab above, select User Guides, Displays, then find your monitor there. Section in setup and troubleshooting may help you. There were many Beige CRT monitors around in '98 of all sizes,so it may be difficult for anyone to help you unless we know the model. Most had a 'reset' or recall button on the front, and that may be what you hit. You will need to go to your on screen menu to adjust.

You are right, I hit the reset button that reset it to the "factory default" so to speak, and screen got dark. I ended up maximizing all settings, including R, G and B at 100%.

If you find you are unable to adjust further from the monitor, double check your display settings properties. Right click on the desktop in the open, select properties, settings tab, advance  button, then choose the color tab. May be you are adjusted there too far (beyond range of fine tuning with the monitor). If you hit default on the color tab it goes to a preselected setting from which you should be able to adjust from the monitor.