New browser window won't resolve

My desktop (XP Pro 32-bit) is having problems resolving browser windows when first opened. This started about a month ago, and it's very inconsistent.

This only applies to newly-opened browser windows.

Existing browser windows, once opened, will load new pages without hesitation. This affects IE7 about 50% of the time and Firefox about 10% of the time.

To get a "working" browser that loads my home page, I sometimes have to open 4 or 5 browser windows at once. Only the last browser or two will successfully load a webpage. The others sit there with a blank screen as the progress bar crawls and the screen remains blank - even if I wait, these windows will never load a webpage.

I use AVG Free Edition 8.0 - checks for viruses and malware (using other software as well) always come up negative.

This is not a connection issue. Every other computer using this router and DSL line works fine. It's something with this particular computer.

What's wrong?