This is a long shot, but can't do any harm, so you might as well try it.
Go to Control Panel > Dial Up Networking. Right click your connection and choose Properties. A configuration box will appear with several tabs at the top. Click on each of the tabs until you find an option "Enable Software Compression" (it can be under any one of the tabs depending on which version of Windows you use) and make sure it is not ticked. Click OK, shut down all windows and restart your PC.
As I say, it is a long shot, but Software Compression has be known to cause the problems you describe with some ISPs. My previous ISP (Fast24) would not load pages at all if Software Compression was enabled - it stayed connected but just sat there.