First, sorry for English
Sounds like a faulty hard drive, corrupt file system, or if lucky, a permissions problem.
Have you tried booting from a livecd and running an fsck on the volume
fsck -A will run the filesystem check on all filesystems on your system
If all is well ...
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WARNING ***
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This is up to you, I take no responsibility if it borks your system.
It could make things worse or it might help
As root
cd to /tmp/
delete .tX0-lock
restart your computer and pray
^^ This can be doen from live cd also
You can also wait for other replies