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You're set at a login prompt, most likely due to a failure in the KDE startup. You can login using your username and password, then you have to inspect your system to see what was wrong. A good starting point is the dmesg command, than you can have a look at /var/log/Xorg.0.log and/or try to launch the graphical environment using startx and take notice of every error message.
I don't know how LinuxMCE works, but if you strongly suspect it is the cause of failure, you can try to uninstall it and restore the previous working conditions. The way to do that depends on the installation method you followed.
Before proceeding a backup of any valuable data is advised (if not already done).