As mentioned by @techie007, there is another thread already at How to diagnose slow booting or logon in Windows 7?. This article mentions using the Windows Performance Analysis Tools, but this link appears to be broken so this is not a viable solution.
Don't give up so quickly though. As the thread also mentions, you can try Soluto, which I use personally to diagnose issues on my laptop. It monitors and makes suggestions about how to reduce start/boot up time as well as remind you about other sysadmin tasks, such as installing Windows or application updates for your installed programs. It monitors computer temperature, antivirus condition, and other system vitals also.
The program BootVis was originally made for Windows XP, but it may or may not work on Windows 7, so give it a spin if you'd like. It was originally released by Microsoft to computer manufacturers to optimize their construction of Windows computers, and has since been discontinued. It offers graphs on CPU, disk activity, etc. of what happens during boot time. Be warned though, it might be too old to work.
Finally, if you don't want to throw any more stuff on your computer, which is probably part of your problem, you can try using the built-in system Event Viewer. The full instructions on how to use Event Viewer to track and diagnose boot times can be found in this TechRepublic article.