Do you have a hard drive? If so you can change your
workbench->prefs->ScreenMode to NTSC 60Hz so it will always boot up without having to use the early startup sequence.
NOTE: If NTSC does not appear in your list of ScreenModes then you will have to move the NTSC monitor settings from workbench->storage->monitors to workbench->devs->monitors
If you use
WHDload you'll be able to change the
tooltype for each game ICON (or once in the global prefs) to include NTSC (get rid of PAL if it is already there) and they will all start and run in 60Hz and thus be compatible with your monitor.
If you dont have a hard drive, and you use floppy disks... you're a bit screwed. You should invest in one (or an
internal IDE->CF adapter and a
CF card).
As for the vertical lines... have you tried changing the
Pixel Clock & Phase settings using the menu on your monitor? Try Auto Adjust first.