I just changed monitors from a 17" Philips to a Samsung 204BW (woohoo!), and was able to boot into Mandriva One just once. After I changed the screen res via MCC** to 1680x1050 (the native for the 204BW), I can't get into the login screen, though I can get to a command prompt with CTRL-ALT-F1 (can't startx, however). I'm running the digital cable from my card to the monitor, if that helps. Thanks for any and all help.

**I did the same procedure on PCLinuxOS and it worked fine, in fact, I'm typing this from my PCLinuxOS install.

Solved by editing /etc/X11/xorg.conf (included "1680x1050" resolution in "Screen" section).

When you changed the screen resolution via MCC, did it run the test successfully? My guess is, even though your monitor is native 1680x1050, the video card may not support the resolution or the refresh rate .

Can try to fix by switching to terminal mode via ctrl-alt-f1. Log in as user, su to root, then enter command "init 3". This will switch to run level 3 and stop the Xorg server. Then can use command "XFdrake" and adjust resolution to a lower setting, perhaps 1280x1024. Test it, save and exit.
Once back to command prompt, exit root, then startx as user. Hopefully this will get you back into the GUI where you can at least troubleshoot more with the new monitor.

Well, I'm back, at 1280x1024. It looks fine, but the fonts look stretched a bit. I can live with it for now. I really appreciate your help, thanks!

Glad you got it going again. I'm sure if you do some research and testing, you'll find a solution to get to 1680x1050. My guess is it's a limitation of your video card and/or driver.

I found with my 19" lcd screen the machine needed 5000 plus bits of memory and my machine was only giving it 4096 bits so X could not start. I don't understand what was happening but the answer was always to go down in resolution and or pixels