Hmm follow this guide carefully, you will need to have a vista home premium iso to get it started.
Make sure you know which button to press at startup to get the boot menu option to select usb-hdd or cd/dvd.
http://www.bleepingcomputer.com/tutorials/repair-windows-with-windows-startup-repair/
http://getintopc.com/softwares/operating-systems/windows-vista-download/
Next you will need this to make the usb work, make sure you have a flash drive that is capable of booting.
https://www.microsoft.com/en-us/download/windows-usb-dvd-download-tool
http://www.poweriso.com/ "avoid the bloatware during the install of this"
If you can get that going go ahead and do so, also when did your computer stop booting up correctly ?
Did you install any...