Type in "cmd" (no quotes). This will get you a small box. Then type in "bcdboot" and away you go.
NOTE: You may have to run it as an administrator. If this is the case, go to "All Programs", "Accessories", "Command Prompt", right click, select "Run as Administrator" to get the command box.
I'd also recommend looking at the excellent tutorial on using BCDEDIT BCDEDIT - How to Use