Can't boot after an update

[DB]

Evening All - at least here in Austria it's evening!

On my other machine, I have Fedora10 (preupgraded from a clean F9), 
initially working with Gnome, but since January happily running KDE.  
For months now, no problems.....

Until yesterday evening!  Applied the recommended updates with Yumex & 
now cannot login.  When I try to login normally, I give in my Username & 
password, the login screen goes away, the little circle woergles away 
and pouf! back to the login screen.

Tried selecting Gnome instead of KDE at the login, nothing appears to 
happen.  At the login window, I cannot specify keyboard nor language.

Got myself to a CLI, logged on as root, edited inittab to start in level 
3.  Login under my normal username is accepted, try startx, screen 
flashes some text (something about authority, I think from the bit I can 
see), screen goes black then comes back to the CLI with several repeats 
of a message about keyboard not compiling, error not fatal, waiting for 
X to terminate.  Logon as root is accepted, gives a grey screen & then a 
Gnome window comes up & seems  to work OK.

Tried the Live CD.  The original non-KDE one works OK, the KDE CD comes 
up to a login window wanting a password for "liveuser" (which it never 
did before - this system was installed from the F10-live-kde disc 
without any problem);  I've tried all the passwords I can think of & it 
just keeps coming back to the login screen.....

Anyone got any thoughts as to what might have happened & how I might get 
past this %&&(%$$ login??

Many thanks (again) for any help

Dave