I don't get any signal from my dell tower to my dell monitor, what can be my problems and howe can I fix it?

Since you say you are not getting a signal I assume the monitor is able to display "No signal". Is it a flat panel or standard older monitor type? If it is a flat panel reboot your computer to the Advanced Options menu (the same menu as safe mode is on). Use the up and down arrow keys on your keyboard to navigate to "Enable VGA" mode. If you still do not receive a signal then your video adapter is probably bad.