My husband has an issue which is not entirely unique, but the fixes which have worked for others are having no impact.
His desktop computer can download email to Thunderbird, but neither Firefox nor IE can browse the internet. We don't get an error, or a "Firefox cannot display this page" or anything, just a white box and "Done" on the message bar. There is nothing wrong with the internet, the other two computers which use the same router work fine. We cannot browse the network between computers.
He is running AVG, which has detected no viruses, and ZoneAlarm, which updated recently, but disabling made no difference. AVG cannot connect with the update servers.
We have inserted values into DNS but then he could not get email, so we set it back to automatic. We have flushed the DNS, cleared the caches, done a number of command line functions involving netsh, uninstalled and reinstalled Firefox, and disabled and enabled the DHCP service. IE offered to run a diagnostic, the summary of which seems to be everything is fine except it gets a 12152 error when connecting with an HTTP site. It could connect with FTP and HTTPS.
Others who have resolved this issue tended to either have Norton installed (this machine has never), was fixed by one of the things we've tried, or have given up and rebuilt their machines. This is considered to be several steps beyond last resort.
If anyone has any other ideas we'd be grateful.