I've had my MacBook for a little under a year and installed OS X Leopard when it first came out. I've had no trouble or issues with it until now. Last night I was surfing the internet and I noticed that everything started to run very slow. Pages weren't loading properly and I had to "Force Quit" Safari several times. Applications, such as iTunes, were running slow as well and took several minutes to even open. Before I went to bed I tried to shut down my MacBook, but the process timed out and froze. I ended up holding down the power button to turn it off. This morning when I restarted, the Apple screen with the rotating disc underneath the logo comes up but won't start up past this screen. I tried powering off and restarting, but the same thing happens each time. The battery power was around 80% when I first shut down. Please help, Im very concerned.