Such a change could corrupt a drive so the first step is to pull the drive and clone it. Now we're safe.
As to the PC BIOS issue, that's a question for the machine's maker or gigabyte. I think this model has a BIOS reset jumper. Try that.
I accidentally changed the settings of my drives from AHCI to RAID and now by PC doesn't boot. I am using a 120gb SSD from kingston and a 1tb wd blue hdd, with a z97p-d3 from gigabyte. I tried entering the bios to change the settings back, but I cannot (tried pressing F2 while the system boots, as said in the MB manual). After a screen where I am told to press CTRL-i to enter the configuration (tried it 1000 times, nothing happens), another screen comes up with the error ''Reboot and select a proper boot device). Is there a way to change the setting back to AHCI and boot normally, without losing any files? Thanks