There might be a way to alt-boot your system. In Macs, you can press the alt-key at start-up to choose your partition to boot.
However, you have to find a way (fdisk might help [I am not such a Windows user]) or the Disk Usage Analyzer of BT5 could give you a hint.
If your Windows-System is still installed, I'd put some external drive on your BT5 and make a raw backup first.
Who knows, your Windows 7 might even be shot dead.