check that your wastegate actuator arm hasn't come off the gate lever pin.
If it has .. it will make no boost because the wastegate will be open and exhaust gas will be vented into the exhaust dump pipe not the turbo housing (making the turbine spin) ie no boost!
or like you say the shaft may be broken, Take the front turbo intake pipe off stuff your fingers into the turbo intake, (motor off, of cause) and see if you can spin the compressor wheel freely it shouldn't have very much movement up and down or latterally just round and round, and definatly you shouldn't here any scraping noises.
this would be a bad thing!
I would put money on that the wastegate actuator arm has come off the pin.
hardest part there is (if it be the problem) is finding a small enf split pin. (or serclip depending what turbo you have) small paper clip will get you out of trouble.
JetGSR
or I could be wrong.