AHCI : Enable in Windows 7 / Vista

Ok, I knew I'd have a hiccup attempting this. During install of my OS a few weeks ago I tried to enable AHCI but kept failing boot so I just stuck with IDE and all has been working well. Figured why not give it a try now that everything is running smoothly. I added a restore point, modded the reg then enabled AHCI in the bios. Upon reboot BIOS starts listing the HD's then as the rest of that particular page is rendering I notice the primary drive listing disappears. Towards the end of BIOS initialization I'm greeted with a notification that no OS is available to boot.

After double checking that I hadn't inadvertently change something I shoulden't have in the BIOS I decided to do a "System Restore" via "System Recovery" off the retail disk. Unfortunately when I get to the System Recovery's option of choosing which OS the apply the restore point to I have no OS to choose from. For some reason it's not detected.

Any suggestions?

Thanks for the welcome!

Nope, safe was my first stab at getting back. Seems the OS is completely AWOL.

I've gone back again and checked BIOS. Everything looks in order in addition to the SATA option being switched back to IDE. Even rechecked all my HD connections since I did have to swap a data drive for a DVD drive because I could never get it to work via USB. Guess I should add the only REG mod was to the "Start" value from 3->0

Cheers!