Sounds like your Mach3 installation became corrupt somehow.
1) No
2) No
3) No
4) Either you were using a modified homing script, which you now no longer have. Or, in General Config, check or uncheck "Home Slave with Master".
For future reference.
When you get everything working correctly, make a backup copy of the entire Mach3 folder.
If you run into a similar problem, do a complete uninstall. See the manual for how to do this properly.
Then, re-install.
Then copy the entire old Mach3 folder over the new one. That should take you back to your fully functioning installation.