Flickering screen
 

I have Acer TM 8104 WLMi laptop with 15,4" WSXGA+ (1680x1050@60Hz) and ATI Radeon X700 and ati-drivers.

My screen has started to flicker sometimes (you can see it easily when you open samething with white background). It flickers often, and when I turn it off, then it may have a very little pause without flickering.

It has not flickered always, and I'm not sure if I've changed something.

May it be because of wrong HorizSync/VertRefresh values in xorg.conf? My HorizSync is set to 31.0 - 83.0 and VertRefresh 56.0 - 63.0. I really don't have manual or anything so I can't check the correct values from anywhere, have tried to Google around it.

Can varying those HorizSync / VertRefresh randomly break my screen? I've tried quite many values there.

HorizSync / VertRefresh generally aren't used for LCDs, so it's more likely a physical problem with the screen itself. The refresh rate doesn't mean anything either as LCDs work in a different way to CRTs and don't have a concept of refresh rate in the same way.

Does it flicker in the BIOS too? If not, then it could be software-related.

It seems not to flicker in BIOS.

May incorrect DPI cause flickering? I've set DisplaySize in xorg.conf to get correct DPI (something like ~128?). I think that's not good DPI since many websites using pt as unit in fonts looks so ugly with way too LARGE fonts. Could I use startx -dpi 100 to get more nice look regardless the correct value, without problems?

Possible, but unlikely. DPI generally just controls what scale things are drawn at on-screen. Give it a try though.

Flickering screen
 

This is probably "stale info," but I went into my /etc/X11/xorg.conf and commented out the monitor's horizontal and vertical rates:

Section "Monitor"
...
# HorizSync 31.0 - 80.0
# VertRefresh 56.0 - 75.0
...

Caveat:
- I use an LCD rather than a CRT: the refresh rates are supposed to be ignored
- I recommend copying xorg.conf into xorg.conf.back (or whatever) just for safety

Anyway, it s-e-e-m-s to prevent the flickering screen that often occured when I would log off and try to re-login.

Best!