So im currently repairing a friends laptop, because when it gets to the windows 7 start screen (just before it loads the desktop) the laptop reboots for some reason and just keeps going this cycle of boot, reach end of boot/prepare desktop, reboot (etc). Ive decided to reinstall the OS... So ive got an old copy of XP to test that but whenever i go to the system tools to install the OS it does not pick up the internal hardive... So I tried to connect and install the os on an external HD (which it did fine) but when it boots I dont know how to get it to boot from the external HD (and thus XP) and not the faulty windows 7 boot instead. Any ideas?