Login dialog doesn't stay on screen long enough to input credentials(resume from screensaver)

I have an old computer which I upgraded the GPU to Mobility Radeon HD 5430 Series, I just installed the modules for Debian Wheezy, but now my screen-saver doesn't work anymore, when I come back to the system, it takes some intuitive key-press to get the login dialog to stay in focus for me to login.

My display manager is KDM.

My desktop environment is KDE.

What I tried, not relevant anymore.(The screensaver runs now, before the screen was black when idle)

I reckon this is because Radeon is turning my screen off.

root ~ # lspci -nn | grep VGA
01:00.0 VGA compatible controller [0300]: Advanced Micro Devices [AMD] nee ATI Manhattan [Mobility Radeon HD 5430 Series] [1002:68e1]

I installed the module with these instructions: ATIProprietary

The only web-pages I can find on the subject are for turning DPM on.

I found this. But it doesn't have anything about turning it off.

Link Link

I've tried this:

sudo su -
touch /etc/modprobe.d/radeon-dpm.conf
echo options radeon dms=0 > /etc/modprobe.d/radeon-dpm.conf 
cat /etc/modprobe.d/radeon-dpm.conf 
options radeon dpm=0

As an attempt to use the settings in one of the answers in here.

I don't know what the problem is, but I'm hoping you know, my problem: when I want to resume from idle(screen-saver running) the login dialog doesn't stay/appear when I move the mouse or press a key to resume from idle.

Do you know what causes this, what is the real problem here?