I have an elderly Inspiron 2500 which has been working well until the last few days.  It now frequently hangs whilst booting up.  It gets as far as the Windows logo with the blue bars moving across but then does not complete loading.  The screen goes blank.  I have tried booting from the disc that came with the machine but am unable to do this.  When I look at the BIOS it suggests that I can not boot from the CD - it has not got a + sign by it.  I am unable to change this in the BIOS setup.  Can anyone help?