Macbook Air Acting funny My friend gave me a macbook air to try to fix it. I'm pretty good with any Windows machine and the common troubleshooting steps. Like safe mode, malware scanners, startup applications and stuff. But I'm not really sure where to start on this macbook air. It doesn't have the dock on the bottom. Hitting shutdown took like a minute for the prompt to come up. So, it's behaving really slow. And I'm sure there's other things, but what should I do to start troubleshooting?

Also, I've noticed the screen go  black for a split second every like 5-10 minutes.
First step would be to try a safe boot per Apple's support pages:


  If you're using Mac OS X 10.2 or later, you can start up your computer
  in Safe Mode, which includes an automatic disk check and repair. A
  Safe Boot, which starts up your computer into Safe Mode, may allow you
  to start up your computer successfully using a reduced version of the
  system software. To do this, follow these steps:
  
  
  Start up in Safe Mode. Instructions on how to do so are located here.
  After the system has fully started up, restart your computer normally.
  


Additionally, you may reference this page of Apple's support pages for other trouble shooting measures to resolve common startup and performance problems.