If it's your PC, and any other machine connected to your broadband is OK, then that narrows it down a lot.
Have you got a proper virus scanner running (eg AVG Free 7.5)? If not...
Have you got anything in your hosts file other than the basics?
Go to C: \Windows\System32\Drivers\Etc and open the file called Hosts in your preferred editor.
If it contains more than a load of lines prefaced with # and a line that says
127.0.0.1 localhost
then remove the extra lines, save the file, and reboot your machine before trying again.
If the engineer could get a proper connection with his machine, and not with yours - what was he doing? Whose engineer was he?