2006 MacBook won't start up

So I was using my early 2006 MacBook (1.8 Ghz Intel Core 2 Duo, tiny amount of RAM) to view a YouTube video, and it froze (gave me rotating rainbow thingy). Since this happens often, I got up to put the computer on the table and do something else. When I picked the computer up, the power cord caught on the table and was pulled off of the computer. Since the battery is 100% dead, the computer shut off abruptly. I've also done this before without trouble. When I go to turn it on, however, now the screen flashes white for a split-second (normal), and I get a gray screen. Eventually, I get a flashing folder with ?. I've tried reseating the hard drive, and pressing down various keys when it starts up, but to no avail. I have a Genius Bar appointment tomorrow, but I was wondering if I could fix it for free...

I'm not sure what OS it is, but it's OS X Tiger, I think.