FC6 freezing at bootup

[Felipe Nunez]

 Hi :
    I recently upgraded to FC6 and I'm very pleased with it, but I've got a 
big trouble.
 Every other bootup with the new kernel /boot/vmlinuz-2.6.18-1.2798.fc6xen the 
system
 freezes during this boot process.

  The las two messages I get are:
       loading uhci-hcd.ko  module
       USB Universal Host Controller Interface driver v3.0

  So, what can I do to safely boot FC6 ?
  

   Felipe Nunez