Generally, the maximum resolution on an external monitor is equivalent to or less than the resolution set for the laptop's screen, regardless of the maximum resolution of the card. The native resolution of the laptop's screen is it. However, it seems that some video cards will allow a CUSTOM resolution to be set that is higher than the native resolution, so that a higher resolution can be fed to the external monitor. However, overdriving the laptop screen could be dangerous. If you can increase the resolution, it would be good to shut off the internal screen.

Thanks for the answer but this is not the problem here. My internal screen is a full HD screen, still I only get 1280x800 on the external display so the problem is not there...

Have you loaded the correct driver for your external monitor(s)?

Thanks for the answer but this is not the problem here. My internal screen is a full HD screen, still I only get 1280x800 on the external display so the problem is not there...

ofocorse.. all drivers are 100%