Have you considered the possibility that your winsock may have become corrupted ?
This can cause connectivity issues.
I would suggest you download the free edition of SuperAntispyware from here:
Once you've installed the software, run a full system scan - which may take a while. If it returns any results of malware and asks if you want to remove the bad files, answer YES.
After that's finished, reboot your computer and see if you can connect to the internet.
If you still are unable to connect:
First, I would suggest you make a new system restore point
Then, open SuperAntispyware and on the main page click on the tab which says "Repairs" on the bottom of the main page. Scroll down the menu until you locate the option for "Repair Broken Network Connection (Winsock LSP Chain). Check the box for that option then click "Repair Checked Items" and follow the directions. After it's over, you may have to re-boot your computer.
This may help solve the problem, since it seems as though you've tried everything else.
You could also do a Google search for Winsock LSP problem in Vista and see what you come up with.
Good luck, and I hope this helps.