If you can connect after a few minutes, then there's probably some junk that's loading at bootup which is taking a lot of time to load.
Go into MSCONFIG, and click on the Services tab. Check the box that says "Hide all Microsoft services". Now check all the rest, then click "Disable all". Now restart the computer.
If doing the above fixed the problem, then there is a non-Microsoft service that was running that was causing the problem.
You could leave all of the non-Microsoft services disabled; but if you do that, some things aren't going to work (e.g. your anti-virus protection). To enable all except the one that caused the problem, go back into MSCONFIG, to the Services tab, and enable everything that you are sure didn't cause the problem. Now reboot. If the problem has not returned, then enable one service at a time (rebooting after each re-enable), till you find the culprit. Leave the bad service disabled, and you should be good to go.