Question on d.mon start=x0 command

[Kazunori Inoue]

Dear Grassusers

Let me ask you  basic questions.

Q1:
I have just installed Grass 4.1.5 (Linux Slackware 3.0). A command d.mon
start=x0 is typed, A message that 'Graph_Set cannot open' appears. What
should I do for it?

Q2:
After I started X Window , I started up Grass. In this case the command 
d.mon start=x0 could be done and a black window appeared. But this window
can not be moved by mouse. What is wrong with me?

Please give me your advises.

Kazunori Inoue