Are you using the latest driver for your video card? If not then update to the latest driver. If you video card is built-in to the motherboard get the latest motherboard driver too.
Also, the options available in the list are for the current monitor. When you connect your new monitor with the PC new resolutions that the new monitor can support will become available too. If you want to see all resolutions that your card can support with your current monitor then you need to uncheck the "hide modes that this monitor can not display" in the "display settings" --> "Advanced settings" --> "Monitor tab".