that might be easier for you:
There is a default X desktop that is installed called IceWM that is always installed in addition to your choice(KDE). Use the login option to select that DE and login into it. If the display works as expected, you can probably eliminate X as the culprit. IOW, it is KDE or a program like PM that starts when KDE loads.
The Graphical User Interface(GUI) is runlevel 5(init 5). It is the normal environment for Mandriva("X starts at boot").
The non-GUI is text mode, the way all servers are setup(or should be ...). Text mode with full user access, all programs that are not GUI-bound running, ...etc. is runlevel 3(init 3).
The system automatically goes into init 3 when "Console Login" is chosen for the (init 5) GUI login screen. It is a KDM "Menu" option. KDM is the login manager(among other things) for Mandriva when KDE is the DE.
To boot to text mode, init 3, all that is required is to edit the kernel boot line options and add a " 3" at the end. The kernel will recognize the 3 as a request to boot to init 3 and thru wondrous magic,
, not start all those GUI-only programs.
You can do that by editing the " Boot Options " for the kernel when the GRUB menu is displayed. That edit is a one time deal - at next boot it goes back to the default.
One can also do that by editing the /boot/grub/menu.lst file. The best way is to copy the lines for the default boot and paste them at the bottom of the file. Then just add a 3 at the end of the kernel line and change the name to reflect it is text mode(init 3).
kernel (hd0,0)/boot/vmlinuz BOOT_IMAGE=linux root=UUID=26213278-351e-4679-939d-5259ce0e09ea resume=UUID=2dbfb2f4-8a8b-4636-99c6-57ca06ba4ca8 splash=silent vga=788
to bottom of file as
title linux init 3
kernel (hd0,0)/boot/vmlinuz BOOT_IMAGE=linux_init_3 root=UUID=26213278-351e-4679-939d-5259ce0e09ea resume=UUID=2dbfb2f4-8a8b-4636-99c6-57ca06ba4ca8 splash=silent vga=788 3
See the 3 at the end of kernel ...line? Note that BOOT_IMAGE was changed also: BOOT_IMAGE=linux_init_3
At next boot the new option will appear in the GRUB menu.
: the boot to init 3 is always a good thing to have in the GrUB menu as there are situations that occur with GUI where one needs to boot to non-GUI, text, mode. E.g., installing some graphics drivers requires init 3 as it cannot be done while X is running.)
After the 2010.1 install, the easiest thing to do is select the "Failsafe" boot option and see what happens with your screen brightness. The "Failsafe is init 1([single user (root) mode] so it won't reflect what happens normally but it should show you if there is a really serious problem with the display(unlikely since 2010.0 works).
I would not bother until after running with init 3 but your choice ...
Don't get too far ahead of self. Just start with IceWM and then if still broken with init 3 and see if everything is OK with display. If so then either X or the PM (or both) are probably causing the problem.
Shutting off(or removing) the PM is the only way I know to isolate whether it is PM or something else. ... You will have to find those programs and either remove them or turn them off. The '' plasma-krunner-powerdevil ''(and the associated '' plasma-applet-battery '' battery saver program) is the only PM I know that is installed by default with KDE. You can safely remove it(& battery saver) by using the MCC Install|Remove SW tool. You can re-install it or another later after the issue cause is ascertained and, hopefully, is resolved.
PS: for anyone reading this, the BOOT_IMAGE=linux_init_3 is just there to make things look uniform as there is no linux_init_3 image to use. It works just fine without it ...