I don't know if this is a problem with something I've done, my PC, or something else entirely. But basically, half of the Linux native games I've downloaded, my monitor refuses to display. Stuff like FreeDroid RPG and SuperTux 2.
It logically must be because it doesn't support the resolution that the game is trying to run at, but I've no idea how to change it or why it's doing this.
Do you have 3D acceleration enabled? Looking at the two example games you listed you would have to have that running to get those to work.
If you used to be able to play these games and suddenly you cannot, then sometimes when you recompile your kernel you have to reload the drivers (example: nvidia drivers under gentoo). Here is what I do to check:
glxgears (if it is on your system) will attempt to show a 3d rendered image of a couple of gears moving around. If you see the gears then you know that your 3d rendering is working and your specific problem may lie elsewhere. This also provides a nice easy way of checking what an expected framerate in a game will be (hint: maximize the image of the gears to fullscreen). glxinfo on the otherhand will just print out information about if things are working or not, and this is generally only useful to those people who know what the numbers all mean already.
I'm not sure what distro you are using, but for gentoo there is a nice tutorial page (as I'm sure most distros would also have) for setting things up.
Gentoo Linux nVidia Guide ? Gentoo Linux Documentation
Additional note: I don't use ubuntu so I don't know if there is a better tutorial than the one I've given you.
glxGears seems to work, and I wouldn't have a clue what that stuff will mean if I try, I suspect... I tried one of the commands from the Ubuntu tutorial too, and that also says that it's working.
Any other ideas?