I tried installing 10.5.7 last night using the regular software update and it kept failing. Then I went to the mac website to download the dmg file, which worked. I installed it fine and then clicked restart. The blue screen came on and the circular thingy in the middle started going around as usual. Then it stopped, but the blue screen stayed. Then the circular thingy came back. I left it alone overnight in hopes that it would fix itself by morning, but no, it's still stuck on the blue screen. Any ideas?