looking for help

Have iMac running OXS El Capitan 10,11,6 mid 2011...get same error while installing expecting value line 1 column 1 char 0...have cancelled and when open safari unable to open any websites get error message this connection is private...called support nice person however unable to resolve...bascially told old computer will need to contact outside company to look/fix...interesting am able to open on safari apple.com however no other websites...

Any one else experiencing this issue and might know fix

Much appreciated