Hey, I had same problem: A friend give me a macbook pro with french keyboard and os in french. I manage to switch the keys around to suit english keyboard. foolishly i formatted with microsoft windows. Ordered a copy of os x online. when trying to boot from disc, i get the three beeps. i troubleshooted with all kinds of method but none work for me:
Here is a simple trick that worked for me:
I borrowed a friend macbook pro of the same kind, took out my HD and place into a external drive and formatted with mac journal format.
attached it to my friend's macbook pro and installed carbon copy cloner on my friend's....
ran the app and cloned everything from his macbook pro's drive to mine through the external.
once completed, place my drive back in and it booted like magic.
only problem, everything will appeaars like the friends.
Just log in and create a new account and delete that friends account.
you might need to uninstall all apps that user purchased and download with yours account