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.