We need some more info to help you.
1. If this a new pc? Store bought or custom built?
2. Was it working ok before this happened?
3. Any power outages lately?
4. Can you move around in the bios to check settings? If so, check to see if they bios detects the hard drive.
So you are saying that once you turn it on, it automatically goes into the bios? It doesn't normally do that on its own, my guess would be you have a stuck key on the keyboard. Try using a different keyboard first.