Since Vista is indeed marked Active and shows up in the Recovery console, it should start with Startup Repair run up to 3 separate times with reboots unless it is corrupted beyond repair.
I would try three more times to start Vista.
If this fails, then decide whether you want Win7 on the same HD for the long term, or to make a partition in the left space of your second HD using Partition Wizard to install Win7 there. If so I would unplug the Vista HD so WIn7 installer isn't confused and creates it's own independent bootloader.
After install when you plug Vista back in , you can browse to recover your files from Vista if they are not damaged too badly. In fact you can Explore for them right now with PW CD, even copy them out now to data drive or DVD using this: Copy & Paste - in Windows Recovery Console
Then you can wipe the DISK0 to clean reinstall Vista, either leaving Win7 HD plugged in so Vista installer creates a Windows Dual Boot, or unplugging Win7 during install so Vista creates its own independent bootloader allowing one HD to be booted via BIOS Boot order and the other via Dell's one-time F12 Boot Menu.
Feel free to ask any questions to decide what you want to do, then we'll give you step-by-step.