Howto solve some of the resolution problems
Integrated Intel graphics card?
Problems with login screen refresh rate?
Backup your configuration file
sudo cp /etc/X11/xorg.conf /etc/X11/xorg.conf_backup
How to edit xorg.conf file
Run in terminal or console:
sudo nano /etc/X11/xorg.conf online help in nano: ctrl+g (ctrl+x exits)
How to edit or add HorizSync and VertRefresh lines
Find your monitors manual (manufacturers website and Google are useful).
Look for hozizontal sync and vertical refresh rates, also if bandwidth or maximum dot clock / pixel clock is mentioned, write it down.
Edit xorg.conf and put correct values to your xconf.org's Monitor section. Something like this:
Be sure that Identifier is same as the Monitor line in Screen section.
Adding custom modeline
Now, if you know what your monitor can do, for example 1024x768@75Hz (edit: choose decent resolution / refreshrate), you can open another terminal window (keep xorg.conf open in gedit) and enter:
gtf horizontalresolution verticalresolution refreshrate
gtf 1024 768 75
Copy paste the output to your Monitor section.
# 1024x768 @ 75.00 Hz (GTF) hsync: 60.15 kHz; pclk: 81.80 MHz
Modeline "1024x768_75.00" 81.80 1024 1080 1192 1360 768 769 772 802 -HSync +Vsync
Watch that the hsync is in range with the HorizSync on the same section (in this example the range is 31-101 and this modelines hsync is 37.65, so we're safe). Also the VertRefresh and the refresh rate you selected (75Hz in this example) should match - in this example VertRefresh is 60-160 and modeline is 75Hz, so that's all good.
Now you can select the defaul resolution and colordepth by tweaking the Screen section. It should look something like this:
Identifier "Default Screen"
Device "NVIDIA Corporation NV34 [GeForce FX 5200]"
Modes "1280x1024" "1024x768"
Monitor name here (CM752ET) matches the Identifier on your Monitor Section. Device line here matches the identifier on your Device section - you get the idea? :) It ties together some settings for your screen - the graphics card and your monitor. You may have more Subsections here, but only one is needed.
Change the DefaultDepth to what you would want it to be, 16 (65536 colors) or 24 (16M colors). Change the Modes line to match the resolutions you want to use - Depth must match DefaultDepth (here it's 16).
Save the config. If you're in X, hit CTRL+ALT+BACKSPACE to restart X (if you're running logon manager like xdm, kdm or gdm). Change between virtual consoles with CTRL + F1 F2 F3 and so on - your X should be on F7.
Starting the X:
startx OR sudo /etc/init.d/gdm start (in KDE it's kdm)
If that doesn't work, try fixing the xorg.conf or get back to your original by copying the backup over your changed one with:
sudo cp /etc/X11/xorg.conf_backup /etc/X11/xorg.conf
When you're back in X, you can cycle through different modes by pressing CTRL+ALT++ (plus sign on numpad), or go to System->Preferences->Screen Resolution.
Where is the log file?
How to reconfigure Xorg
You can do the whole X configuration process by entering:
sudo dpkg-reconfigure xserver-xorg
Why must I set the correct screen resolution on every startup?
How to ask help
personally I prefer to help on these problems if the question is asked on correct forum on its own thread, it makes answering a lot easier (than trying to remember everyones nick, GPU, monitor and so on). It will also give more attention to your question as more people will read it.
Helpful information you can add to your post when asking help on this subject
What are the symptoms
Do you get only low resolution
Do you get only black or distorted screen?
which monitor do you have?
make and model
link to specification sheet or user manual, if possible
which graphics card do you have?
chipset, amount of memory
some parts of /etc/X11/xorg.conf -file
Beginning of Screen-section (~10 lines)
resolution you want to use
attached /var/log/Xorg.0.log (compressed preferred), *NOT* INLINE
:!: Things to try:
vesa driver instead of your graphics card specific driver
nv instead of nvidia
16-bits colors instead of 24-colors
adding HorizSync and VertRefresh line in Monitor section with correct values from monitors specification
adding custom modeline for your monitor in Monitor section
online modeline generator (http://xtiming.sourceforge.net/cgi-bin/xtiming.pl)
gtf generator online: http://www.sh.nu/nvidia/gtf.php
sudo dpkg-reconfigure xserver-xorg