[XFree86] Resolution not setting automatically

[U M A R]

After  installing debian in one pc connected to the monitor it sets resolution automatically.So i disconnect that monitor and attach some Projector and booted my OS then its not automatically setting resolution.If i tried to reduce or increaase the resolution its not showing any other resolution options except 640x800.So how  can i make OS (debian based) to autoconfigure for any monitor connected at the runtime.

Everytime giving dpkg-reconfigure xserver-xorg   is very tedious
Any other alternative................

    Regards:
     U M A R
  

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