You experienced an event called BSOD (Blue Screen Of Death). It is a feature of Windows operating systems just like the Windows logo at startup (only slightly less frequent).
If it has happened only once and you can't reproduce it then just blame it on sun spots and get on with your life. If it happens often or you can reproduce it then post back and give us more details like what exactly were you doing and exactly what gibberish (if any) was printed.