Richard - from your description, it appears to be a hardware problem with a simple fix:

1. For problems with peripheral devices that are natively supported by the BIOS (SATA and IDE hard drives and CD/DVD drives, floppy drives etc.) there's a basic rule of thumb: if the BIOS don't see it, ain't nobody gonna see it.

2. If the BIOS doesn't see it, it's a cabling problem about 90% of the time. Always double-check and/or swap the cables first. Make sure every cable is securly connected.

3. SATA cables are especially prone to poor connections (just look at the design; it ain't rocket science). I've found that the best way to overcome this is to secure the cable itself into position with nylon cable ties, such that the weight of the cable is not pulling on either connector.

As an aside, I would strongly suggest that you not return to that computer shop. Amateurs.

Jon