Hi
You still have the two options ( external enclosure or re-install )
Probably best to try the Recovery Disk and re-install the Operating System.
You said earlier that you have a disk - simply pop this into the CDROM drive and switch on.
If it doesn't "see" the disk you need to tap F12 and select CD/DVD from the options.
Follow the information on screen.
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If, for some reason, there is a problem and the installation stops it could be the hard drive itself.
If this is the case then we do need an external enclosure so that we can test the drive.
There is another option that uses a CD - you would need to burn this from an ISO download.
Seatools - click here