12" display problem with Beagle Board

hi

I got up Angstrom Linux running on Beagle Board ver B7 board and the
monitor is 19" Benq DVI-D. its working fine with resolution 1280x720
@60

i changed the resolution to 800x600@60 on Benq monitor and it works
fine but
When i connect a 12.1" Color TFT-LCD with DVI-D input display and set
the resolution to 800x600@60 the monitor does not work..
when the beagle board is powered on the beagle logo is also not
display..the screen is just blank.please let me know what could be the
problem

the 12.1" display supports 800x600@60 resolution which i have checked
on normal computer and it works well without any problem

the monitor supports 24bit color i.e. 16.2M colors according to
datasheet
will i have to adjust the Hsync and Vsync frequencies or the frame
rate, if yes then how to do that..