I am a newbie CNC user, and had everything on my G0704 running smoothly. Then, today, I launched the software to cut a piece and it gave me two errors. The first telling me I didn't have Pokeys installed (though the PC came with it installed and it worked perfectly the day before); and second, that the Mach IV software "The screen set "Screens/wx4.set" does not exist.
I can't launch anything... help.

This has happened because the profile you use has corrupted typically due to shutting down the PC without closing Mach4 properly.

Go into the Mach4Hobby installation folder, open Mach4GUI.exe, select the profile you use from the list and then select 'Restore Backup' button on the right. From the list select the profile that is the oldest as it is most likely to work and then restore.

 Hopefully this works for you