Oracle Database Discussions

i've oracle 10 g installed in my comp on windows....
till now it was working fine....
but now... when i start database n try to access tables through
home - > object browser - > show tables ..... it's not showing any tables
or
home - > sql -> sql commands -> select * from tab
(in this case ... there is not even run option to run the command )


however i can see tables through Run Sql Command Line ... (the console)

does anyone have any idea...

thank you