i hope i'm right in this solution.
boot no startup sequence,
at the command prompt, type
delete sys:prefs/env-archive/sys/screenmode.prefs
and that will delete the custom setting for screenmode. will force the machine back to the default of pal or ntsc, which ever's your base setting.
---edit---
doh! how do i set it to no smilies? "sys: prefs/blahblahblah" - without the space
