Did you tried tinkering with the options inside dosbox.conf?

Fullfixed, fullresolution and such.

I did, same thing. You see, my laptop HAS this possibility, that is rotating the screen by pressing Ctrl+Alt+arrow. For some reason, it invokes the feature when trying to run dosbox in fullscreen. Thanks for your interest anyway.

Did you by chance swap width and height in your "fullresolution" option? And did you use your LCD's physical resolution?

If your native (maximum) screen resolution is 1024x786 pixels, use exactly that in fullfixed. Your laptop shouldn't be able to rotate that 😉

I think you mean 1024x768.

Common LCD resolutions are 800x600, 1024x768, 1280x1024, 1600x1200

Of course I meant that, thanks for the correction 😉
And you forgot 1280x800 (widescreen) and 1400x1050.

Oh yeah, forgot about widescreen LCDs since I've never used one

I finally made it, thanks to help from eL_PuSHeR and Moe:
This is my conf now:

[sdl]
....
fulldouble=false
fullfixed=true
fullresolution=Default
output=surface
hwscale=1.00
....

And to get "real" fullscreen on the laptop:

[render]
frameskip=0
aspect=true
scaler=advmame3x

😎 😎 😎

Good to hear you got it solved but I would use frameskip=1 - You won't hardly notice any difference and will save a few cpu cycles.

😎