invalid group name / home directory changed

[ktb <x.y.f@home.com>]

I don't know how but every file and directory has recursively changed in
my home directory.  What has changed is group and owner of all files. 
they are all now "1000".  

I can change the owner to "kent" but not the group.  When I try to do
that I get - "invalid group name 'kent'".   I looked in /etc/group and
there is a line - users:x100:
I added kent -
users:x:x100:kent

Still can't change files in /home to group "kent".  

I do not know what I could have done that all the files in my home
directory would change in such a way.  How could this happen?  How can I
add group kent?  How can I do this recursively to the whole directory?
Thanks,
kent