I've been using a Vertex3 SSD as my Windows 7 boot drive in IDE mode for a few months without problems with a ASRock A75M-ITX motherboard.
Today, I ran the Microsoft fix-it to enable the AHCI drivers, changed the SATA controller to AHCI mode in the bios, and rebooted. It gave me the message
BOOTMGR missing. Press CTRL+ALT+DEL to reboot
So I went back to the BIOS and saw that my SSD is no longer listed in the boot priority menu. However, it shows up and boots fine if I press F11 to bring up the boot menu during the POST and select it. The first time I did this, Windows told me the AHCI driver was installed and I should reboot.
Currently my computer is usable, with all indications that the SSD and Windows are working properly in AHCI mode, but the drive will not show up in the BIOS boot priority listing, although it is listed elsewhere correctly. I failed to find any BIOS updates for my motherboard on google.
Is there something else I can try?