My external hard drive is disconnected. How can I open my local disk C with tools?

My computer is off, and we disconnected the external hard drive. It is currently in my garage. I have it near a power outlet, but can't find the right cord for it :[! I can't get ahold of my dad either for help. There is an important disk in one of the local disk C that I need to get out. How can I get open without power? Can I use tools, like a screwdriver, or something? Please help :[[[