This is what I would try. No guarantees! Pure speculation on my part, so make sure you have essential data backed up.
Boot up again with your Windows 7 installation dvd. Go through the initial windows as usual and select custom install. Assuming you can then see the HD, select it as your choice for installation and select the option to format it.
Now back out and reboot and see if it identifies the HD. I am not certain, butthe only problem this might create is a change around of partition letter assignations. You can solve this problem by, once again, using the DVD and selecting the repair start up option.