You need a boot disk to install Windows onto a new hard drive, the two things go together. Do you have a USB flash drive in the laptop? If you do, remove it and check things again. Then make sure the drive is seated properly, remove it and re-install it in the laptop. If that did not fix it, see if it's seen in the BIOS, if it is, check the boot order and set the hard drive first in the order. If that does not work but the hard drive is seen OK, you may be able to just run a Repair setup of Windows, if you made a restore disk when you got the system. If you did not make your own set of disks, contact ACER for help. They would also be able to tell you how to run a disk check to see if you do need to buy a new hard drive, or maybe just get one from them of the system is under warranty. If the drive is bad, just doing a new Windows setup won't help you, you have to replace the drive then install Windows.