FC 17 needs several logins before desktop works

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http://forums.fedoraforum.org – On my FC 17-65 XFCE Spin system with noveau video driver, the following problem has cropped up: I boot and login as an ordinary user. The XFCE desktop appears. I click the mouse on something and the desktop vanishes. Instead of the desktop I see the printing from the last text boot screen. Usually the login screen reappears, but sometimes I just stay stalled on the text screen. At the new login screen, I login again and the process repeats itself several times. When the desktop screen vanishes, I cannot use Ctrl-Alt-F2 to get a useable console. Ctrl-Alt-F2 produces a black screen without (HowTos)