it will not login

Hi i have a G5 with Lion instaled. When i first turn on the machine i get the apple symbol and the bar underneath. It takes about 5 mins for the bar to fill then the login screen comes up. after typing in the password the screen goes white then back to the login screen again.

i ve tried to reload Lion but cannot do it as it tells me the hard drives are locked.

The machine works on Bootcamp on windows side.