Trouble switching virtual consoles

I'm having difficulties with getting virutal console switching to work correctly. If I have my external monitor connected to my laptop, it boots fine into a text console, and I can start X from there. Then once X is running, if I switch to a virtual console the text has gone "wavy" and I can't read it, looks like a problem with refresh rates. If my external monitor isn't connected and I try to switch virtual consoles when X is running it just crashes! In fact if I even try and shutdown the computer when my external monitor isn't connected, it dies! Very frustrating as you can imagine... The same thing happens not matter what window manager I use..

My graphics card is a Nvidia Geforce 4 420.

Any ideas on how to fix this? Your help is much apperciated. :-)