maybe your friend changed the config in the CMOS. you can check it by pressing f2 or delete upon the POST (power on self test) check IDE drives if it is disabled or changed.

it is quite difficult to teach you how to fix that one since this is a case to case basis. Is your pc using an IDE HDD or a SATA HDD. I am just assuming that your friend forgot to return the settings back before he/she used it.

it is quite easy to fix that unless you have a broken hdd, broken cable, or broken ide/sata controller. just ask if there is anybody here who is near your place that is adept in pc troubleshooting.