WHEN I TURN MY NETBOOK ON IT SAYS " REBOOT AND

What OS?

First - re-seat the hard disk and reboot the computer. If the computer does not boot up then reboot and go into the BIOS configuration to see if the BIOS detects the hard drive. If it doesn't detect the hard drive then it could be faulty.
Then the hard drive needs to be replaced in the computer/laptop, Windows installed and the computer or laptop's device drivers plus your programs etc. to get a functioning computer/laptop again.

check whether the hard drive is detecting or not, select the first boot device as hard disk

This problem can be caused by 3 things.
1: Fault Hard Drive.
2: Faulty cables or connection.
3: Faulty motherboard.

As it is a netbook I would recommend taking it to your nearest PC repair shop and asking them to test your HDD and motherboard.

Go to more than one place so that you do not get ripped off.

-Regards
-Mitchell

or check the bios settings . look in to which drive is the first drive

In this case you need to repair your OS. You need to insert the OS which is a bootable disk, in case of net book you need to connect a USB with OS loaded in it and select boot from USB in bios, for entering in bios you need to press the F 2 button while restarting the computer.

You have to install it using a usb drive...(cdrom, memory stick, etc...)

The proper boot device is your hard drive, when you boot hit F2 while it is booting up and it will bring up the screen to change boot devices select the hard drive and save the settings and this should work if it dont it is possible that your hard drive has bit the dust.

B52computers

you need to insert the os disk and select the auto repair function to direct the boot manager to the correct path of your os

Insert a Bootable Opearating system CD
Reload Your Operating System if Problem persist change your hard disk
Load the Operating System