Takze odzkousel jsem u sebe nahodit 100Hz natvrdo pres modeline pro 1024x768 a jede to OK.
Takto u me vypada sekce monitoru

Kód:
Section "Monitor"

    Identifier  "mon1"
    HorizSync   30-95
    VertRefresh 50-160
 Modeline "1024x768" 103.42 1024 1056 1152 1280 768 770 774 808  # 103 MHz, 80.8 kHz, 100.0 Hz


EndSection
karty

Kód:
Section "Device"
    Identifier  "8500le"
    Driver      "radeon"
    #VideoRam    65536
    # Insert Clocks lines here if appropriate
EndSection
a potom a hlavne mel byt v teto sekci uveden spravny monitor a karta.

Kód:
Section "Screen"
    Identifier  "Screen 1"
    Device      "8500le"
    Monitor     "mon1"
    DefaultDepth 24

    Subsection "Display"
        Depth       8
        Modes       "1280x1024" "1024x768" "800x600" "640x480"
        ViewPort    0 0
    EndSubsection
    Subsection "Display"
        Depth       16
        Modes       "1280x1024" "1024x768" "800x600" "640x480"
        ViewPort    0 0
    EndSubsection
    Subsection "Display"
        Depth       24
        Modes       "1280x1024" "1024x768" "800x600" "640x480"
        ViewPort    0 0
    EndSubsection
EndSection
Pokud to takto nemas tak si to oprav, treba pres xf86config je to textova utilita ktera vygeneruje novy XF86Config.

Take je jeste otazka jakou mas GK, pokud mas radeona a fglrx drivery tak to musis vygenerovat pres fglrxconfig a nejlepe nen stary XF86Config smazat, vytvori se novy XF86Config-4.
Pokud mas nVidii tak tam ti moc neporadim, nemam ji.

Takze at to shrnu bych nejdrive projel XF86Config jestli je cely OK, pak zkontroloval drivery ktere tam mas a podle toho vygeneroval novy XF86Config a dal tam novy modeline a pak to uz musi na 100% fungovat

EDIT: ted se divam ze u toho HorizSync mas chybu misto 700 by tam melo byt asi 70.0