I have a 2010 iMac and had installed OS X 10.12 Sierra on it with no problem, but now as I'm using the computer my iMac constantly freezes, sometime it will operate for a couple of hours then just freeze. Nothing happens? I have no idea what is going on. I have re-installed Sierra, did the recent 10.12.1 update, but no changes??? This is driving me crazy! I can have 3 or 4 freezes in one evening of just reading my favorite web-site articles in Safari. It usually happens while I'm in Safari browsing my favorite websites. I have no idea what is going on and never had this problem with OS X 10.11. Any ideas?