I wonder whether the Poll should specify which Mini or ask to list which computer had HDD problems.
One thing about the Dell Diagnostics partition and the way it reseals itself after the first boot, if one boots to that partition the first time it is ever booted it can prevent the OS from ever booting (without some changes). Remnants of that process could be at the root of what is being seen here.
For me, I've had no problems with several builds of W7 on Mini 9 (Runcore), three Mini 10's (using Samsung, Hitatchi, Seagate, OCZ Vertez SSD
), two XPS M1330's (using Samsung, Seagate, WD, OCZ Vertex SSD
), and two XPS 420's (using Hitatchi, Seagate, WD, OCZ Vertex SSD
). Even an old Dell 8100 for kicks. I think in all cases but one, I installed W7 on a wiped-clean HDD with no Diags. partition. That one case was a dual-boot with the original XP.