I recently had this issue. My SSD is my boot drive and every now and then, it would start up like that. I later had to rebuild it due to moving and found my HDD stopped working. After a little work, I found the issue was the power cable from the PSU.
So before going out and buying yourself a new HDD, just try using a different power cable and if that works, then you'll have no issues. I would suggest also making sure to back up your data as soon as possible in case it is the HDD.