I've got a brand new iMac and I loaded Big Sur beta on to it and it seemed to work fine for a while. Now it is crashing about every 30 seconds after booting up. I've tried every conceivable fix I can think of and then some. I've attempted to reinstall Catalina but the install program can't find the internal hard drive. The icon does not show up. I'm hoping an update will solve the issue, however, today I reinstalled Big Sur and got the same results. Any ideas?