Did you update any packages like X itself, your display drivers, desktop tools that control your display etc.? If you did an update before your last boot, better read your logfiles about what was updated
it might help.
Become superuser (root), open a text editor of your choice and open up file
/etc/X11/xorg.conf. There should be listed the available refresh rates so see if they are ok (and before editing the file, check out when it was last edited; perhaps before your last reboot?) If the file does not contain any refresh rate options, and you know your screen's horizontal and vertical rates, you can add them there yourself: inside the Monitor Section, (if there aren't already), add
Code:
HorizSync horizsync-range
VertRefresh vertrefresh-range
where
horizsync-range and
vertrefresh-range are the given ranges, respectively. This is what
man xorg.conf has to say about these two:
Quote:
HorizSync horizsync-range
gives the range(s) of horizontal sync frequencies supported by
the monitor. horizsync-range may be a comma separated list of
either discrete values or ranges of values. A range of values
is two values separated by a dash. By default the values are in
units of kHz. They may be specified in MHz or Hz if MHz or Hz
is added to the end of the line. The data given here is used by
the Xorg server to determine if video modes are within the spec-
ifications of the monitor. This information should be available
in the monitor’s handbook. If this entry is omitted, a default
range of 28-33kHz is used.
VertRefresh vertrefresh-range
gives the range(s) of vertical refresh frequencies supported by
the monitor. vertrefresh-range may be a comma separated list of
either discrete values or ranges of values. A range of values
is two values separated by a dash. By default the values are in
units of Hz. They may be specified in MHz or kHz if MHz or kHz
is added to the end of the line. The data given here is used by
the Xorg server to determine if video modes are within the spec-
ifications of the monitor. This information should be available
in the monitor’s handbook. If this entry is omitted, a default
range of 43-72Hz is used.
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