I am signed into my iCloud account on four separate devices: iPhone 5s, iPad mini, rMB, and MBP. Today, my Contacts disappeared from my MBP (10.10.5), so I went into System Preferences -> iCloud and I noticed that the checkbox next to Contacts was not checked. I tried to check the Contacts checkbox but it will not allow me to. The checkbox is not grayed out or anything. When I click the checkbox it will stay checked for a second and then it will go back to being unchecked. I tried restarting the computer several times, reset PRAM, signed out and then back into iCloud, etc. but nothing has worked so far. My iCloud contacts are still on my other devices and I can see them through iCloud.com. I did not change any settings on my phone or other devices to cause this to happen. No matter what I do I can't enable iCloud Contacts sync on my MBP running the latest version of Yosemite. Thank you in advance for your help.