After I change my screen resolutions to 1600x1200, X boots into a black screen.
I have a Dell Latitude C840. I remember setting the HorizSync to 59-85 and VertRefresh 40-90 by google (I couldn't find the information anywhere on my manuals).

Anyway, I can ctr+alt+f1 to console but got no idea what to do next. any help will be greatly appreciated!

-complete noob

At the command prompt try xf86config

I got command not found

Well maybe it's not in your $PATH. Try entering the full path with the command
/usr/X11R6/bin/xf86config

1600x1200 on a laptop? Are you certain it's capable of displaying that resolution? Can you do it in windows?

Yep, that's my LCD's natural resolution. RH9 refuses to work in 1600x1200. Aggghhhh

What chipset does your video use??? Is it the Radeon 7500 series like in the C640???

I have the geforce 4 440 go

Try this to get you to a starting point at the cml

XFree86 -configure
XFree86 -xf86Config /root/XF86Config.new
cp XF86Config.new /etc/X11/XF86Config

If you see a blank sceen with an X cursor, type ctrl-alt-backspace to get back to the terminal

or before you do the above, go to /etc/X11/
and see if you have an XFree86Config.* and just copy that file to XFree86Config.
Basically everytime you make an adjustment, the old XFree86Config file is save as XFree86Config.*

Hope this helps

At command line, find and cd to #etc/X11
edit XF86config using vi. (find instructions on using vi) it is very simple, there are four commands you need to know.
to open the file, vi /etc/X11/XF86config

[ i ] inserts text
[ esc ] exits insert mode
[ :q! ] abandons all edits and exits to command line
[ ZZ ] saves all edits and exits to command line
always remember to [ esc ] , and all commands are case sensitive.

change horiz to 49-70
change vert to 49-70
Change size to 1024*768

startx, then if it fails
keep changing these settings until it works.