All my power windows stopped working, could it be the master switch?

could be.could be a fuse.could be that window lock button is pushed to lock.

Another quick & easy test you can make is get in car and leave the door open so the dome light stays on . Turn key to the on position, do not start engine .. CLOSLEY watch dome light as you try to operate the windows .. Does the dome light dim 'just a tiny bit' as window switch is actuated? .. In a quiet environment, you may even hear the window motor trying to turn or click each time the window switch is used .. Post test results for more information.