It sounds like you're trying to do a "upgrade" install. Correct?
ZoneAlarm will leave traces in the registry and other places.
You might try downloading PC Decrapifier, it's free program designed to wipe out all traces of programs and such.
Go here:
http://www.pcdecrapifier.com/download
You might also try Smarty Uninstaller 2009, it's fully functional for 15 trial period and does a great job of finding traces of old programs left behind after an uninstall.
Go here:
http://www.winnertweak.com/download.html
You might want to try doing a custom install or what's known as a "clean" install. You'll find that clean installs give you much better results than doing the upgrade install.
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