HDD sometimes can't be detected, what could be the problem?

HDD sometimes can't be detected, what could be the problem? the HDD or the Mobo? anyone encountered this?? my system is still under warranty but i don't want it to spend the week at the shop so i want to know the possible problems first so i could tell them and immediately fix it.

Ive had a similar problem before, it turned out to be a faulty data cable.

Hope that helps. Rik.