Grbl is not an alternative to mach3. Actually it doesn't have a user interface, it's just a motion controller that takes gcode input and turns it into pulses to drive stepper motors. There are front ends that can drive grbl but so far as I've been able to find nothing that has the functionality of Mach. And if you're having trouble getting mach going you won't find grbl easier.
Though I suggest linuxcnc that is probably harder to get going. I'm fairly sure that it can be downloaded with its own version of Ubuntu, so no need to have a real time Linux distribution.