Lately, lots of users have been emailing with support requests saying that MAMP's Apache refuses to start for them, even if they try and start it using MAMP's control panel. This seems to happen immediately after they let VirtualHostX make changes to MAMP's httpd.conf file (which it does to enable virtual hosts).
This fix for this is surprisingly simple.
If MAMP isn't starting for you from their control panel, make sure MAMP's Apache port number matches what you have setup in your virtual hosts in VirtualHostX. By default, MAMP is set to run on port 8888. If you keep that default, all of your virtual hosts will need to be set to 8888 as well. Or, you can change everything (including MAMP) to run on the more standard port 80.
Make those changes and then try restarting MAMP again.