Originally posted by: Buz2b
Drop back ten and punt! Seriously, it could be something simple or a combination of simple things. Had something similar once and solved it with a combination of putting in a new CD drive, cable and BIOS settings. First things first, I'd put in a different CD drive although it sounds like you might have tried that. Do it with a different cable and MAKE SURE you check the jumper settings on the drive (Master, Slave, Cable select). Make sure you go through and unplug, then re-plug BOTH your IDE cables. Sounds silly but do it. Then go into the BIOS and do two things: set it to "Default Settings" and then make sure that the BIOS recognizes each drive (optical and HDD) in the correct configuration; meaning Master/Slave and IDE1/IDE2. If you do these, along with changing out the CD drive (take yours and put it on hers for this attempt) and for some reason it doesn't work, try flashing/re-flashing the BIOS.
The problem you're describing doesn't really fit the symptons of a bad MB, so stick with it and see if you can solve this.