Bios Switches boot hard drive?

OK weird problem. This has happened 4 times in as many months.
Turn the computer on and no hard drive. My first thought ok need new drive no big deal. But in the bios I noticed the drives there just that the #1 drive is now #3 so I switch them back and everything is ok.
Has anyone ever heard of this. I called ASUS and 1st person says battery but all the other settings do not change. Second person says power supply but this doesn't seem right.
Any thoughts?

Asus P5Q Pro
Intel quad 9550
Sapphire 5850
4x Sata 750gb
Xigmatech 750 watt
8gb ram corsair dom.
win 7 pro 64bit
4 answers Last reply
More about bios switches boot hard drive
  1. A dead Bat could definitely do it. But for a easy fix just switch the cables on 1 and 3 :)
  2. Welcome, Newcomer. If your CMOS battery is failing, it could be reseting any changes made to your BIOS. A good way to test this is to "load optimized defaults" in your BIOS. If the boot order changes back to HDD being third, this may be the cause. With HDD as priortiy 3, your boot order would probably be 1. Floppy, 2. CD/DVD, 3. HDD, 4. USB or other external device.

    A failing PSU can explain why a hard drive doesn't power up, and subsequently doesn't boot, but I can't think of any reason why a failing PSU would change your BIOS settings.
  3. And go ahead and replace the battery while you're at it. These are supposed to last about 10 years, but in real life...
  4. I will try the battery.
    When I say it changed from 1 to 3 I mean the hard drives #1-4. My boot sequence is 1 DVD, 2 HD#1.
    I will also switch the sata ports and change the # hard drive to what the bios wants.
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