The next step to diagnose the cause of the problem would be to prevent all unnecessary programs from starting when Windows starts and then running in the background.
The only aps that you need running in the Windows startup menu are your av ap and your firewall.
I recommend Startup Inspector to manage your startup menu as it is much easier to use than msconfig, the Windows utility.
Startup Inspector (manages startup menu – helps you identify aps in the startup menu so you can disable unnecessary programs from running in the background when they are not needed)
Startup Monitor (a small freeware ap available on the same page to notify you and require your permission for any program to add itself to your startup menu)http://www.windowsstartup.com/download.php
Disable all unnecessary program entries
Clicking on an entry will highlight it and inform you what it is connected with in the lower right pane.
After disabling unnecessary aps reboot, and if the time it takes for the computer to boot is back to normal, reopen Startup Inspector and enable one item you unchecked at a time and reboot continuing until you find the one causing the problem.