I bought a Lenovo B570 laptop today, and one of the first things I did was burn an Oneiric LiveCD and install it. This was more trouble than I expected. It didn't automatically load to the CD when I restarted; it just booted Windows 7 like before. I had to press F12 at boot and use a very unintuitive menu to get to the LiveCD.

So now I've installed Ubuntu and restarted, but once again it's just booting to Windows like nothing happened instead of showing the familiar GRUB menu. What's going on here? (This is my first Windows 7 computer; my previous one had Vista dual-booted.)

EDIT: I should clarify that I can't load Ubuntu at all. Or at least I don't know how to.