I have Debian intalled on my laptop and it worked fine. Then I needed to update some packages and I did: apt-get upgrade
It downloaded the new packegs and installed them.
But, next time I tried to log into Debian, I couldn't get to the login screen ... I got the message:
Display server couldn't start (or something like that) 6 times in last 90 seconds, I will wait 2 minutes before I try again.

And really, it waits for 2 minutes, and then tries to display the login screen (6 times and it fails each time) and again the message appears.

I still have the 'MS-DOS'-like prompt and I can login, but it would be nice to have my old Debian desktop back.

You can try dpkg-reconfigure xserver-xorg as root. Then select your driver (or VESA). If you're using Nvidia's or ATI's proprietary driver, you probably have to rebuild the module.

When I do that I'm getting:
Package 'xserver-xorg' is not installed and no info is available.

Under /var/lib/dpkg, in file 'available', I see the packages xserver-common and xserver-xfree86
I guess, these packages were affected by the upgrade ... Is there any way I can simply go back to the previous version of these packages?

I looked at the /var/log/XFree86.log and here are the lines with warnings (I included a couple of surrounding lines as well):

...
(**) |-->Input Device "Generic Mouse"
(WW) The directory "/usr/lib/X11/fonts/cyrillic" does not exist.
Entry deleted from font path.
(WW) The directory "/usr/lib/X11/fonts/CID" does not exist.
Entry deleted from font path.
(**) FontPath set to "unix/:7100,/usr/lib/X11/fonts/misc,/usr/lib/X11/fonts/100dpi/:unscaled,/usr/lib/X11/fonts/75dpi/:unscaled,/usr/lib/X11/fonts/Type1,/usr/lib/X11/fonts/Speedo,/usr/lib/X11/fonts/100dpi,/usr/lib/X11/fonts/75dpi"
(==) RgbPath set to "/usr/X11R6/lib/X11/rgb"
...
...
(++) using VT number 7

(WW) Open APM failed (/dev/apm_bios) (No such file or directory)
(II) Module ABI versions:
XFree86 ANSI C Emulation: 0.2
XFree86 Video Driver: 0.6
XFree86 XInput driver : 0.4
XFree86 Server Extension : 0.2
XFree86 Font Renderer : 0.4
...
...
(II) LoadModule: "int10"
(II) Reloading /usr/X11R6/lib/modules/linux/libint10.a
(II) VESA(0): initializing int10
(WW) VESA(0): Bad V_BIOS checksum
(II) VESA(0): Primary V_BIOS segment is: 0xc000
(II) VESA(0): VESA BIOS detected
(II) VESA(0): VESA VBE Version 3.0
...
...
(II) VESA(0): initializing int10
(WW) VESA(0): Bad V_BIOS checksum
(II) VESA(0): Primary V_BIOS segment is: 0xc000
(II) VESA(0): VESA BIOS detected
...
...
(==) VESA(0): Write-combining range (0xc0600000,0x1b0000)
(==) VESA(0): Write-combining range (0xc0400000,0x3b0000)
(WW) VESA(0): Failed to set up write-combining range (0xc0000000,0x7b0000)
(II) VESA(0): virtual address = 0x4028f000,
physical address = 0xc0000000, size = 8060928
(==) VESA(0): Default visual is TrueColor
...

What version of Debian are you using? xfree86 was last used in Sarge, I believe, which had support ended recently. Anyway, you can try dpkg-reconfigure xserver-xfree86 instead.

Ok, I tried it. It didn't work, but thanks anyway, pljvaldez.

Could you post your /etc/apt/sources.list? Xfree hasn't been used since Sarge, as pljvaldez said. The upgrade from Sarge to Etch has always been a bit spotty due to the xfree to xorg switch, and if you sources.list has entries for "stable" instead of only "sarge" entries, then it will attempt to upgrade to Etch. The worst scenario would be if some lines had "stable" and others had "sarge". Then you'd end up with a mishmash of Sarge and Etch versions, which will really mess things up.

Yeas, that is a possibility. The thing is, I installed Debian from CD, and then when I needed to update some packages, the versions that I needed were not available on the CD, so I modified the sources.list file and specified the HTTP URLs (but I'm prettty sure they were pointing to the unstable sarge sites) so apt-upgrade can pick up the latest versions from the web.
But anyway, I simply reinstalled Debian, and now I will update these packages individually ... I won't use apt-upgrade, that's for sure.

This is a very unique problem as was stated before, since the X windows was upgraded from the Xfree86 system to Xorg, and that just never went smoothly through apt.


Just download the newest installer (for stable or testing, whichever you prefer, personally id go with testing unless its a mission critical server that doesn't care if the packages are a bit outdated)
It will have Xorg and all that installed. Definitely ditch that old installer CD.