Like I was mentioning before you may have seen a bad install of 7 where something didn't go on fully as it should. The lack of seeing the drive in the bios however is a hardware or bios concern with a drive known to be working however.
As far as cables coming loose while not having moved the case or opened it? You have case fans blowing cooler air into the case I hope as well as good circulation. When finding the end of the drive cable here was lifted up in the port on the board that was a little bit surprizing as well since all cables are reinspected at times to insure they are all in properly. Somehow it still lifted itself causing the drive to vanish until finding it that way.
The next question of course would concern any trips made into the bios setup throughout the 7 installation for things like any settings changes made. If you post screen has a full screen logo disable that in the advanced in order to see the post tests list all drives detected at startup to see if it shows there.
Did you make any boot order change in the bios during the installation for booting off of the 7 dvd or bring up the boot device menu using the assigned F key at post time?
These are the things anyone would be asking. A cable can be plugged in firmly and still go bad on you being another possible cause to consider. This is why the idea of rechecking things over never hurts to insure some small item isn't the cause. You can think you can have everything ruled oot and still see a few surprizes at times.
OK, first, that is why I have been asking for help on how to go into the BIOS and fix it because I already know all of this, and it becomes clearer to me that people are not reading.
Second, since I had to yank the cables pretty hard when testing them to get them out, I doubt that my fans could effect them... I mean honestly... think about it.
Third, no trips were made to the BIOS when I installed Win 7.
Fourth, no boot changes were or have been made.
Fifth, I'm a pretty thorough girl when it comes to my hardware, when I say I checked things, it means multiple times because I'm also anal about it. Almost 90% of my work and at least 90% of my recreation is centered on my computers, so telling me to recheck things I have already triple checked is no less annoying than the tech support person telling me to unplug my modem, wait 30 seconds, restart the computer, and plug the modem back in again after I had already done it about 10 times before calling them. I realize there is no way you could have known this about me, but can we please get off the hardware?
How do can I fix this in the BIOS?