Hard Device Change at Restart

I have 2 internal hard drives in my notebook.
Disk1 is my library (documents, etc.) with no boot files.
The boot is in Disk2 with my operating systems.
Sometimes when I leave my computer open for video editing, etc., when I open it, I see that it has restarted, and waiting with flashing _ on the black screen.
When I check the BIOS, I see that the hard disk device order has changed from Disk2 to Disk1.
How could this happen and why?
Is there any way for me to learn why the computer has restarted itself?

The first step is to check your Event logs for any errors or reasons for the reboot. You'll also find out the exact time the reboot occured.

If you mean by updating BIOS from ASUS Flash, yes, I did.
I will check the BIOS Updates on ASUS.
ASUS has an auto update program, but it never worked on my computer (and many others).
It always tries to download the same file.

Thanks for the event logs information. I needed that.
Is there any place I can learn to use Event Logs efficiently?
How do I see the restart time? (Hope will figure out soon).
I googled it, but couldn't figure it out yet.
Anyway, thanks for the information.

Maguscreed said:

Was I wrong in thinking we needed to address the hardware address issue?

Not necessarily, but checking the event logs would tell you if it was hardware or software. I'd be nervous about doing a BIOS update if I found out that the board had faulty memory, a faulty power supply, or was over-heating...all of which could cause the spontaneous reboots. That's why I suggested the event logs...so he'd know why the reboot occured.

IMAyNeed said:

Is there any place I can learn to use Event Logs efficiently?

There isn't really anything to learn, to be honest. The events are broken down by type...system, applications, security, etc. Then they are listed by chronological order. The errors will stand out as soon as you open up the Event Viewer.

I suspect a weak/failing CMOS battery....Part # CR2032...available anywhere.

I will check the event logs and inform you guys.
Thanks for your replies.

Addition: I still couldn't find any restart errors yet.
But still will keep you update when I find it or if it happens again.