on some PC you can make a set of recovery DISCS from Vista - I know the new HP machines do, as i have istalled a couple recently
also some PC have a partition you can access and reload the software by pressing a key on boot again on an old HP it used to be F10
Why do you want to re-install - it may be possible to fix, also a restore may work for you
If you re-install you will lose all data and any programs, updates you have installed and it will take the machine back to the condition it was in when you purchased it
Have a read here
http://www.acerpanam.com/synapse/dat...or%20%20DT.pdf
<Alt> + <F10> during the boot-up process,