check this out , may help you to fix your problem http://www.bleepingcomputer.com/download/fixexec/
I've run that batch file and this is what it reported, although it doesn't mention .zip.
FixExec by Lawrence Abrams (Grinler)
http://www.bleepingcomputer.com/Copyright 2008-2015 BleepingComputer.com
More Information about FixExec can be found at this link:
http://www.bleepingcomputer.com/download/windows/utilities/fixexecProgram started at: 08/05/2015 08:36:10 AM in x64 mode.
Windows Version: Windows 7
Checking for processes to terminate before fixing executable associations.
* No processes found to kill.
Resetting .EXE, .COM, & .BAT associations in the Windows Registry.
* HKLM\Software\Classes\.exe\shell found and deleted!
Program finished at: 08/05/2015 08:36:37 AM
Execution time: 0 hours(s), 0 minute(s), and 26 seconds(s)
I'll need to see if I can find the thread in the other forum which had the .zip I had been trying to open.
If it hasn't fixed the file association, would 7-Zip open it automatically or do I have to associate 7-Zip with that .zip file ?