In Task Manager/Processes click on Memory and that will sort to the highest user first.
It could be your AV program but if it's a service host then right click on it and select Go to services and whichever is at the bottom will be the culprit of that, but see if you still get the slow start in a clean boot.
Go Start - type msconfig - press enter and under the Startup tab click on Disable all - Apply - OK - Restart.
If that gives some improvement but not all, then under the Services tab, check the box to Hide all Microsoft services - Disable all - Apply - OK - Restart, but ensure your antivirus program is still running.
If there is an improvement with either lot disabled, then you will need to enable one item at a time under Startup and check the start up and if most improvement occurs with the non-MS services disabled, then you can enable a few at a time, restarting after each selection.
To revert to a normal start up, check the button for Normal startup
You could also run a command prompt as an admin and see what a chkdsk /f has to report and also check on the fragmentation status of your HDD.
You can view the full chkdsk log in Event Viewer by expanding Windows Logs - click on Application - Action - Find - type chkdsk or wininit into the Find box and press Enter.
Cancel the Find box and then read the report in the scrollable window.
One more thing to try that I can think of at the moment if none of those has resolved and that is to boot up into the advanced boot options - select Repair your Computer and navigate to the Recovery Environment to select Command Prompt and enter bootrec /fixmbr
Enter exit to close the command window then Restart
There is a Startup Repair option in there but it rarely fixes anything and as long as the machine eventually boots up, it doesn't think anything is wrong.
In msconfig under the Boot tab, check the button for OS boot information and the next time you restart you can see the drivers loading and if it is sticking on anything.
You can also create a Boot log by checking that button as well and the log can be found in C:\Windows as nbt
Double clicking on that will open it in Notepad but it can be confusing by saying such and such a driver hasn't loaded when a previous entry has said that it has - it can't load twice.
To revert to a normal boot, just uncheck those items under the Boot tab in msconfig.
