Just switch the bios back to IDE. That should stop the rebooting. If not, boot into safe mode and set the registry entry back to what it was before. If you don't remember what it was, do a system restore to yesterday. I've used this method before and know it works. Did you use the fixit or manual instructions? I'd use the manual instructions.
To resolve this issue yourself, enable the AHCI driver in the registry before you change the SATA mode of the boot drive. To do this, follow these steps:
Exit all Windows-based programs.
Click Start, type regedit in the Start Search box, and then press ENTER.
If you receive the User Account Control dialog box, click Continue.
Locate and then click one of the following registry subkeys:
In the right pane, right-click Start in the Name column, and then click Modify.
In the Value data box, type 0, and then click OK.
On the File menu, click Exit to close Registry Editor.