Not sure if this is the source of your problem but Mach3 will not allow jogging before homing if soft limits are turned on. Turn off soft limits and you can then jog. Maybe you turned on soft limits by accident?

Personally, I keep soft limits on all the time as I like having that small safety net in place, but my machine is not so big that homing takes a long time. I also wired homing switches on X and Y to separate inputs so that I can home X and Y simultaneously which saves a bit of time when homing.