If there was a RAID check, most likely one of your drives is in bad shape.
If it was only one of them, you may be able to boot from a single drive if you had a mirror set.
If you are stuck, try booting to drive 1 and if that fails, booting to drive 2. If neither work, you may be in trouble. What error codes is it throwing.
If you CAN boot to one drive alone, immediately back up your data. We see this frequently, where there is a reliance on a mirror set to be the full level of fault tolerance for irreplaceable data, and that is a ticking time bomb.
I personally have a USB drive plugged into the back of my NAS and I run nightly backups to it. Short of my physical location having a problem (water leaks, fires, etc) I can survive a catastrophic loss of the NAS in the event that it happens (which it eventually will, no electronic device lasts forever, and you cannot predict failures)
It may not be a comfort to you should you experience data loss, but I believe this trend is the result of the explosion of data that average users retain and this kind of technology becoming more mainstream; out of the data centers and into the home, as it were. Backups that don't share any single point of failure have long been a standard in the IT space, but easy to overlook in a personal home setup.
I wish you luck.