but not under these circumstances so I don't know if I can help.
IE will still connect to https and FTP even if it is set up to connect through a Proxy. But not http.
In IE, goto Tools > Internet Options > Connections tab, and check through any Settings and LAN Settings buttons. Has a Proxy been set up? If so, perhaps changing that to "Automatically detect settings" would fix it.
If that does the trick, then your next task is to find out why those settings are being changed. The last one I saw with this the user had recently been Income Tax accounting software!
If it is not that, then I must pass and leave this to others to consider.
I recently upgraded Internet Explorer on the PC at work from version 6 to version 8, and after working fine for a while, it stopped connecting to almost every webpage that i navigated to. This PC is the main office computer at a U-Haul dealer, and all of U-Haul's website (that we use for renting trucks, etc.) worked fine, which confused me.
When the network diagnostic is run, it says that windows can't connect through HTTP, HTTPS, or FTP. Disabling the firewall does nothing to correct this problem. What's weird is that windows CAN connect through HTTPS and FTP; that's why Uhaul's site worked fine. I can access anything through HTTPS, like my Gmail account, clickbank, Uhaul, etc etc, and when I tried ftp.microsoft.com it worked as well. A normal HTTP page such as google won't connect.
If i shut down the computer, unplug the router, wait, plug in, and turn on the computer, Internet Explorer WILL connect to sites like normal--but eventually, it stops, and I can't connect with HTTP again!!!
Oh, and i uninstalled IE8 and went down to IE7 and updated everything, but have the same problem. GAH!