Unable to login in to either Yahoo or Gmail email accounts. Also, same problem when attempting to login to any "https" site. Have disabled my firewall program (ZoneAlarm) as well as many other things (overrode cookie restrictions in both my browser and firewall settings, e.g.). My first suspicion, given nature of problem, is that ZoneAlarm (first edition, which I uninstalled and re-installed) has some lingering entries in my registry or such that is not being reset using conventional means. Have run CCLEANER to check my registry as well. My next recourse assuming I am not able to pinpoint problem is to reload Windows XP. Any interim, less austere recommendations are appreciated.

Did you set Yahoo and GMail as Trusted sites?

HI,
Try this; but not absolutely sure it will solve this issue.
At any site, click on Tools and the top, then Internet Options.
Click on the Security tab. Then, click on the Custom Level button.
Reset to: Medium (if it's set to High).
Click Apply and OK.
I hope this helps.

If you mess up a zonealarm install/uninstall it will almost definitely leave trace blocks in place. Had a similar problem with it. Had to re-install and uninstall. If this was recent, a sys restore may be easier if zonealarm continues to fail during installs, if that was a symptom.