Xwindows configuration

[Linda]

I have a machine that everytime it starts a new xwindows 
session, ie a user logins, the login screen it will start to 
draw the screen and than go blank for several seconds and 
then the display will appear. I turned on all the messages 
in Xdiagnose and reading the syslog it looks like X tries a 
monitor setting and then changes to a new one. Just 
wondering where I look for the configuration files to tell X 
windows to just start with the second settings? I haven't 
played with X windows configuration files for a few decades 
and am not sure where to start looking.
                          Thanks
                          Linda