Yes.
Keep tapping the F8 key until you see a black screen and white letters. You will see some commands like "Safe Mode" or "Repair Computer" choose repair and it will take you to a menu it will than give you more options one would be restore to factory settings or restore to a previous point. etc.
Get Linux!
There are no boot floppies for Windows Vista. To install Windows Vista, computers must support either booting from a DVD or over a network.
Windows boot manager controls how your computer will restart again. One example is to boot after going to sleep. Another example is to boot after pressing the reset button.
...with Windows XP Professional already installed on your computer. Windows Vista cannot be installed without Windows XP Professional installed first on your computer, it's the same with Windows 7; Windows' latest operating system (OS).
Repair Your Computer
How do I boot up my Laptop windows vista because it will not start up?
Let them date
Unless you have to, it is many times advantageous to œwarm boot, or rather warm reboot, Windows . In a warm reboot, Windows restarts, but the computer doesnt, skipping the whole pre-Windows boot scree/BIOS/startup sequence. You an easily specify a warm boot in both Windows XP and Windows Vista. Just hold down SHIFT on your keyboard before clicking œRestart in Vista, or before clicking OK in the restart dialog in XP. Enjoy the extra 20 seconds!
When you boot up just watch the screen and if it says 'Windows Vista' anywhere on it, then your operating system is Vista.
No. Windows Vista is not based on DOS and a DOS boot disk will be unable to read the file system that Vista is on.
Yes, you can but you have to check the hardware part of your computer. Also you need the upgrade version to keep your files and programs, otherwise you have to format.
You can find here all required information http://www.howtogeek.com/howto/windows-vista/fixing-bootmgr-is-missing-error-while-trying-to-boot-windows-vista/