When my Windows 7 is slow when booting, I do this:
Start, then in the searchbox, type run. In Run, type in "msconfig"(without quotation marks), and click on OK.
In the general tab, make sure selective startup is selected.
Under Selective Startup, click to clear the Load Startup Items check box.
Then go to Startup Tab, and disable everything except antivirus programs and important programs such as microsoft program. Also, DO NOT disable any program that you do not recognize.
This will disable all unnecessary background programs and prevent them to start on boot.
NOTE: you can still start programs even though they are not starting at boot. E.G. let's say your favourite game is one of them, and you disabled it. Now, the game will not start on boot, but if you click on the game icon later, it will still start, except it may be a little slower when it starts. Basically, you are delaying the start of programs that does not need to start at boot, you are moving a part of the booting time back. The only programs that you shouldn't disable is programs that actually needs to start(like if it does not start your computer's gonna blow up or something similar).