in Planet Linux OpenSource Debian Software ~ read.

Enable serial console on Debian 'sarge' GNU/Linux

At first, you need to enable serial ports in your BIOS and wire them up to the case front (if they aren't allready).

Make sure you have the following in your /boot/grub/menu.lst:

serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1
terminal --timeout=10 serial console
# kopt=root= ro console=tty0 console=ttyS0,115200n8

Check that "ttyS0" is in /etc/securetty, remove /etc/ioctl.save, if its there.

Last change goes to /etc/inittab, add there:

T0:23:respawn:/sbin/getty -L ttyS0 115200 vt100

Now you can use a terminal program like minicom with 115200 baud, 8n1 and no flow control set.

Have fun and much luck on recovering your machine!