LR 2015 R14 not logging into my account.

I run LR2015 R14 (Classic) on an iMac 2007 with OSX10.10.5 Yosemite.  Has (had) been working well for many years. Now logged out of my account and Develop module disabled.  My login email does show in the help menu of LR.

Problem:  Am unable to install ACC successfully. Goes into endless loop,  asks for a repair and fails that.

How can I install ACC for my OSX 10.10.5??

Many thanks for help and advice on this..