Octave can't see its own functions?

[Maxim Düster]

Hello,

I installed Octave 2.9.10 from source with Cygwin on WinXP. Everything 
is ok, Octave runs, built-in functions work properly, but neither of the 
functions in the 'share\octave\2.9.10\m\' directory does work:

octave:3> dir
error: `dir' undefined near line 3 column 1

octave:4> help plot

help: `plot' not found
Additional help for built-in functions and operators is
available in the on-line version of the manual.  Use the command
`doc <topic>' to search the manual index.

octave:5> doc plot
parse error:

 syntax error

>>> doc plot
           ^

All the .m-files are there. What should I do?

Thanks,
Max