Sounds like the HDD die. If you haven't make a backup disk, then sorry, you lost your data. You need to get professional data retrieval.
Get ASUS to swap out the HDD, you are still under warranty.
ASUS don't provide data recovery and they have to take your old HDD back to Seagate to claim a new HDD for your warranty. So, before sending it ASUS, ask them what procedure you need to get the old HDD back so you can send it to the data recovery.