If your computer is only slow at startup it is likely that there are a lot of applications and/or services set to run on windows start up.
This is likely the result of installing applications on your PC/laptop.
When my PC is slow to start, I check the following.
1) Under “Control Panel\All Control Panel Items\Programs and Features” were there any new programs installed around the time the slowdown started? If so I uninstall them and see if that cleared it up.
2) Verify that the Startup folder only contains apps I want to start when I boot windows.
3) Use regedit.exe to verify the following registry keys only contain applications I want to start when windows starts. (Exercise caution here, remove the wrong things and your PC may not work as expected)
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Run
4) If I still have a problem I sort through my windows services to see if there are any set to "automatic" that I don't want running.
This is an effective way to remove bloatware and improve the speed of your PC.
That said if you bought your PC within the last ten years or so and you really want your PC to boot faster. Consider replacing your system hard drive with an SSD. The difference in speed is ridiculous even on a “slower” PC and the price has really come down.