I don't know if this answer will be helpful to the original poster seeing as this question appears to be a bit old but in case someone else needs this info, here's my two scents. First, my unit is an Asus X502CA notebook/laptop with a 320 GB HDD from HGST. I recently went through a similar ordeal. I spilt quite a bit of water on my laptop which ended up causing it to boot into the AMI (American Megatrends Inc.) BIOS rather than into my OS - Windows 10. After doing a bit of ultimately unhelpful tinkering with the Aptio Setup Utility, here's what I did that actually fixed the issue for me;
Sorry, if this is long – I wanted to be as thorough and precise as possible.
1. Turn off the unit and unplug all cords, USB devices, external drives, etc.
2. Wait for the system to power down completely (takes about 10 seconds - you'll notice all lights on front of unit are off) and then flip unit upside down.
3. Open the unit's chasis by removing all screws. Flip the unit upright again and peel the keyboard and palm rest up until removed.
4. Unplug the two ribbons connecting the keyboard to the motherboard/mainboard by flipping up the little gray or white locks securing the ribbons. Set keyboard aside.
5. Assess the inside of the unit for water damage and do you best to dry it out by allowing a non-shedding towel to soak up the water. Just set the towel down and press gently - DO NOT RUB. A blow dryer on low/medium may also be helpful.
6. After everything is fairly dry, move on.
7. Remove the hard drive and set aside. Remove the battery if you think it may have gotten wet, dab dry and replace.
8. Open your HDD by removing the screws which secure the circuit board to the bottom of the drive and gently dry the inside of the drive out with a paper towel – DAB, DON’T RUB. If the cushion on the inside of the drive is wet, remove it and let it dry.
9. After the drive is as dry as possible, you can let it sit for a while and air out if you have doubts. Otherwise, re-assemble the drive and reinstall it into the laptop. * Note that I do not suggest you remove any of the screws on the top side (labeled) of the HDD. Doing so could void any warranty you may have, so unscrew them at your own risk.
10. After reinstalling your HDD, replace your laptop’s keyboard and palm rest and reboot the unit. If you have set up an admin or user password via the BIOS options, just enter your passcode and hit “enter”.
11. Now, if it still doesn’t boot to Windows (or your installed OS), reboot the system, enter password again (if applicable) and immediately after hitting enter, start pressing the ESC key repeatedly until a menu pops up. This menu should ask you about booting options (I don’t remember the exact phrasing) you should see your HDD and/or OS in the list. Toggle to it and hit “enter”. Your system should then boot to the OS. Problem solved!