screen size problem

[VadimB]

hi all,
I have a 19'' minitor but X shows only on part of the monitor(somthing like 17'')
If I change the resolution it changes only in the 17'' box and the refrash rate is bad.when I change xorg.conf to my screens real horizontal /vertical rate X wont boot and I have to restore it. Its probably the driver, how can I set it up?
In windows xp it works just fine.
tnx

[VadimB]

this is my xorg.conf

Section "Device"
Identifier "VESA Framebuffer"
Driver "vesa"
#VideoRam 4096
# Insert Clocks lines here if appropriate
EndSection

When I change VideoRam to 16384(my real memory) X wont boot

# DefaultDepth 8
# DefaultDepth 16
DefaultDepth 24
# DefaultDepth 32

When I change it to 32 it wont boot also