When the computer boots into the graphical login screen, you can press CTRL+ALT+F1 to get a textual login. There you can login using username & password, after which your shell starts (if it doesn't start bash but another shell, you can change that in the /etc/passwd file -- look at the last field).
Then bash will notice it acts as login shell and will execute the commands in .bash_profile.
You can even get other terminals by pressing CTRL+ALT+F2 etc. and in most distributions CTRL+ALT+F7 will be the graphical screen.
It is possible to prevent the graphical screen from coming up when booting, but this is very dependent on which distribution you use. For example, in some distributions you can boot into runlevel 3 (type a "3" on the prompt of your boot manager) and you will not get the graphical login. But, again, this depends on which distro you have.
Hope this helps!