Option 1: Open Task Manager > click startup tab > Disable all and enable 1 by one until you find whats causing the slow startup.
If on the fist reboot with nothing you have installed loading on startup and its still booting slowly. It will be a Windows issue so...
Option 2: Start > (type) MSConfig.exe > services tab >tick "hide all Microsoft Services > disable all > reboot > enable one by one until you find the culprit.
The second option is longer but more thourgh. Hope this helps.