I dont know what the problem is but sometimes a temporary solution until your friends car is checked is u can turn the key untill all the lights on the dash turn on but without turning on the engine. Then you should be able to shift it into any gear from there most of the time. Hope that helps at least to be able to move the car around to a mechanic or wherever u need to go.
My Old 2004 V6 Mustang 3.9L
15.9 sec @ 88mph
2008 - May 2009 R.I.P.
My Current 2001 V6 Mustang 3.8L
17.0 sec @ 83mph
August '09 - Now
Both were stock during those races