So I was excited to install El Capitan Beta 4. On my first Mac, I installed through Apple's sign-up program and all went fine (although only through Beta 3), but on the second one, I downloaded Beta 4 directly using a link posted here on MacRumors. Big mistake! First, I didn't realize until the thread below that I could just click on the App Store...Purchased tab and download it on my second and third Mac. Rather, I used the direct link posted here on MacRumors to begin directly downloading first the firmware and then the fourth beta. Now I can't get my second Mac to behave. It originally would just power off about 40% through the restart process. Now I've created a bootable drive through my WD Passport external drive. But I still can't load my backup, erase my second Mac drive, or load Yosemite on it via the web. It tells me it is unable to unmount the drive. Any suggestions?