Can't leave X Windows

[Eric]

Hello all:
I am using Debian Potato, and recently installed the X Windows system.
However, I can no longer go back to the command line. I tried Exit, and the
other various exit/kill commands. I also tried Alt-Ctrl-F1. When I do this
the monitor goes out of frequency. I am absolutly positive that I set the
correct frequency in XConfig. Any ideas?