Dell Inspiron AHCI can't detect hdd

[gabiz_ro]

I've managed to build a custom pci option rom for my Dell inspiron 9400 to switch ICH7 controler from compatible to sata ahci mode.
PCI registers looks ok but at boot time bios report my hdd as is was detected in legacy mode and now controller is switched to ahci so all programs can't access my hdd.
But if I boot into linux (from usb stick) I can see and get access to my hdd without problems.and is in ahci mode because hwid is changed to 8086:27c5.
I need somehow to let bios redetect my hdd or something else to have hdd available after bios post.
How can I do that?

[edwin]

pretty simple. if you installed windows without ahci mode and now are trying to use it in ahci mode it has the wrong driverset loaded for that. reinstall windows and don't forget to feed it the drivers from floppy during the F6 stage of the install.