>In the Project Manager I try to open tables as follows
>
>1- Select "DATA"
>2- Select "DATABASE"
>3- When I press + sign against DATA1 then nothing happend but computer hangs and I have to restart it.
>
>When I open tables separately by double clicking from main directory then all tables open correctly.

Looks like your DBC may be corrupted. What happens if you openit from the command box:

OPEN DATABASES MyDatabase EXCLUSIVE
VALIDATE DATABASE

If that works, I would suspect your project as being corrupted. If the project file is corrupted, you can delete the .PJX/.PJT files and rebuild it again.
If the database (DBC) file is corrupted then the best bet is to try from a backup. Else using a table fixer utility might do it. Worst case you might have to rebuild the DBC (losing long names in fields, permanent relations, view definitions, etc.)