The file mode has no effect on whether or not the owner can chmod a file.
$ chmod 000 foo
$ ls -l foo
---------- 1 chris chris 0 May 6 13:55 foo
$ chmod 700 foo
$ ls -l foo
-rwx------ 1 chris chris 0 May 6 13:55 foo
You probably have bad permissions on the parent directory -- at the very least, your user needs the execute permission set on the directory to change the mode of files inside.
You can find more information about how directory permissions work at "Why do directories need the executable (X) permission to be opened?".