A serial console will save you from lots of trouble. It is basically a redirection of all kernel messages from screen (where you'd expect them to show up) to a serial port. The tricky part is that a serial port needs some configuration and setup, which of course needs to be finished beforehand.

To start serial console output, append "console=ttyS0" (or something like that; serial port's name depends on your hardware) to the kernel's command line. If you don't set any other options, 9600 baud, 8 data bits, no parity and one stop bit is assumed. There's no handshake enabled.