Have an original Xbox? If so, you probably need to remove the clock capacitor in it. Unless you have one of the latest motherboard revisions, you need to remove the capacitor, otherwise the capacitor could bust and leak fluid all over the motherboard (and obviously you don't want that).
Here is a reddit thread with some more details to reference: https://www.reddit.com/r/originalxbox/wiki/clock_capacitor
Go to the "Removing the Capacitor" section to see what your clock capacitor should look like (it depends on your motherboard revision).