You need to take the computer to a repair technician to restore Windows 7 on the computer, if you have warranty service on it. The c655 will not work on any Windows OS older than Windows 7.
I tried to do the same thing for a store owner friend's computer, but NO DRIVERS EXIST for anything below Windows 7 for Sound, Video and Wi-fi on the Toshiba c655. You may be able to trick out access to the video by linking up the internal INF files, but that's it.
Sorry, but the Toshiba c655 is a Windows 7 computer, flat out.