laptop "internal hard disk drive not found"

I will describe what I have done to date in detail, to minimise the usual to-and-fro questioning:

My daughter has an Inspiron 1545, with a corrupt hard drive (WD Scorpio Blue 250GB). It would not boot into Windows (W7 HP), subsequent boots reported missing OS. I have found this is usually a loose or damaged drive or/with corrupt windows files.

Naturally, there are no CD's to help with the recovery...

Removed it and tested it - multiple bad sectors,etc, etc. Not worth spending time on.

So, I replaced it with a new WD Blue 500GB (this laptop will take up to 640GB, I believe)  - this is a mm or so slimmer in height than old drive. I formatted & partitioned it (NTFS, C & D) via another computer.

First attempts to fit into laptop reported  "internal hard disk drive not found" -perhaps it wasn't seated, as I didn't feel it "click". After much fiddling, I managed to seat it without the mounting tray & bezel.

This time it recognises the drive - phew! The BIOS (ver A14) also shows a 500GB drive in place.

So I install W7 Pro without a problem (making certain the laptop isn't moved, as the hard drive isn't secured!)

I downloaded all relevant drivers for the laptop onto a memory stick, and as a first move, updated the BIOS, and rebooted.

Oh-oh.  "internal hard disk drive not found"

Removed drive, installed into a.n.other laptop - boots fine into Windows.

Re-inserted drive (still without mounting tray, etc) and booted using a Linux LiveDrive CD. This has no problem reading the drive and its contents.

I have tried re-seating it a few times, have trawled the forums for ideas (see above actions), but now I am stumped.

Any suggestions?