Dell Latitude D600 (PDF)
It's an old Pentium M laptop.
"will not boot up" actually describes a range of issues. Can you be more specific? Does it begin to boot up? Do you see something on the screen?
Or does nothing at all happen when you press the button?
If there's data you need on the hard drive it might be best if you get that cloned before you try any sort of repair... although with an older laptop there may not be a lot you can do.