I'm writing this since since the symptoms manifest as and was sparked by problems with my harddisks.
It all started with me waking up to a computer that had frozen during the night. As the symptoms (failure to boot from harddisk, the harddisk not showing up in BIOS) pointed to a dead harddisk, I ordered a Seagate Barracuda 1TB harddisk. After installing the harddisk I went into the BIOS to check that the harddisk was found (it was).
But as I got to the windows 7 install, the harddisk didn't show up as a possible location for installing (nothing did as it was the only attached harddisk). I rebooted the machine and checked the BIOS where the harddisk no longer showed up.
I could get the harddisk to show up again, in the BIOS, by unplugging the computer and waiting for a bit before plugging it in and turning it on again. It would however disappear again on following restarts, and not show up again untill I unplugged the computer and waited again.
When the harddisk did show up in the BIOS, asking the BIOS to auto-detect it did not make it disappear.
Allowing the machine to boot up the windows installer after having had the machine unplugged did not make it show up in the installer.
Attempting the above with the disk I assumed dead did not make show up.
All of the above was done while in IDE-mode. The harddisk does not show up in ACHI-mode trying the same procedure, though it seems you can only access the BIOS at a later stage in the boot-up process while in this mode.
The motherboard is a ZOTAC geforce 8300
As a sidenote: When in IDE-mode, only channels 0, 2 and 3 shows, skipping 1, with the IDE optical drive showing on channel 0 and the harddisk on channel 2 when it shows up not sure if this was always case as only just noticed it.
So any ideas on how to get it working would be appreciated, or some idea as what would need to be replaced.