Can't login from GDM

The quick answer is no, there is no default password.

However, it sounds like your keyboard settings for X differ from those settings for tty. Are you using a non-US keyboard, i.e. an AZERTY keyboard from example, or numbers in your password on a French keyboard? There are a couple of things you can try:

• Look at the log files to see what the errors are being thrown up, when you try to log in to the GNOME login;
• Change your password to something where the keys are always the same on any keyboard layout, for example uiopkj;
• Copy your .xinitrc file to .xinitrc.bak, and delete all the lines in the original .xinitrc file. Run startx with the empty .xinitrc file. Now try to test your keyboard layout setup.

You probably just need to ensure that the keyboard layouts in tty and Xorg are the same. I've had this happen to me many a time, when I was a locale test engineer, using loads of different "foreign" keyboards. Most frustrating.