At which point of the boot process is it getting locked for that time? During the "DELL" logo? During the "Microsoft Windows" loading bar? Before or after one of those?
In case the problem is with the "DELL" logo or near that, first make sure you don't have any device connected via USB (or other kind of port) during boot. A friend of mine had a problem where, if her phone was connected via USB to her laptop, the laptop would take 30 min to boot up.
If this does not help you could try to update your BIOS. Go to the manufacturer page for driver downloads and select the last version for the BIOS. For Dell, enter your service tag here, you will find that service tag attached somewhere on your computer:
Select your OS and download the latest BIOS version. Please notice that (in my opinion) this kind of BIOS update should not be done unless something is not working properly (as it is with your computer).
Also you could try a static discharge. Power off your machine, unplug from AC, remove the battery, and press repeatedly the power button for 30 seconds. Also repeatedly press all keys on your keyboard. Then put the battery again in place and plug the computer to AC and see if the problem persists.
If problems begin during the "Microsoft Windows" loading bar, then probably running a System Restore or using your recovery partition to restore your computer to factory settings is the best you can do.
Else, if you computer lags during session login, try disabling as many startup programs as you can:
If you need any more help ask us. If you solve your problem, please reply back with your solution.