Your MAC Address won't just change on it's own... Not if you're using the same network card. MAC Addresses (Layer 2 Physical Addresses) are "burned in" to the network card. There are ways of changing them through software, but if you haven't gone through and changed ti there should be no change.
What was the 'previous' adressed and what is the 'new' one?
IT Blog: .:Computer Defense:. PnCHd (Pronounced Pinched): Acronym - Point 'n Click Hacked. As in: "That website was pinched" or "The skiddie pinched my computer because I forgot to patch".