A common problem when trying to solve an issue with your Mac is understanding just what has happened, and being able to explain it to yourself, or anyone who may try to help.  Here is an excerpt from a blog titled Tech Tails by Small Dog Electronics that lay out some basic steps for troubleshooting your Mac.

Troubleshooting your Mac: A Guide to Narrowing it Down By Moses Laporte

As a tech, I have a unique perspective on the Apple world and the underlying factors that contribute to faults in our technology. It seems to me that the majority of issues that I handle day-to-day are often quite straightforward fixes, and yet it becomes difficult to translate that experiential knowledge into relatable and useful information that customers can use to build their own troubleshooting skills. Therefore, I am reaching out in this article to try and explain some common issues that find their way onto my bench, and how they might be diagnosed properly. A customer who is informed about the inner-workings of their machine will always experience more straightforward and reliable service from repair depots, and find that being armed with the right amount of experience makes resolving issues far less painstaking. This workflow reflects many of the steps I follow in order to track down points of failure in the event of malfunction.

Here are the basics:

Write down your symptoms, in the CORRECT ORDER. When does the issue occur? What steps does the machine complete successfully? Make a checklist from power-on to full OS boot, and figure out specifically where the issue begins to show itself. This is key in identifying whether a problem is software or hardware based.
Ensure the machine is backed up completely, ideally with Time Machine or a disk cloning or sparse image software. If the machine is not able to boot and you do not have a backup, it is imperative that you have the technicians recover the drive information before any repairs are done to your machine. Creating a copy of those files as quickly as possible can make the difference between losing your data or saving priceless information.
Isolate Software-based issues. Once your data is securely backed up, attempt to resolve the issue by reinstalling your operating system via Recovery Disk, USB installer, or Retail OS X DVD. If you are not comfortable with this process, we are happy to provide the service for $45.
Once you have completed an OS refresh, if the issue persists, your machine may have hardware trouble. In this situation it would be best to have it examined by a trained Macintosh technician who is certified to disassemble and perform repairs on your model of Macintosh (that’s where small dog comes in!). Be sure to include as much detail about the issue as possible, including pertinent environmental details: How many other devices are connected to this machine? Have you experienced power-related issues such as a brownout or power surge in your home’s grid? Are there other sensitive electronic devices in the area that may be causing interference?
These are important factors in tracking down suspected issues. To ensure that your machine is diagnosed and repaired in the smoothest and most effective way possible, making sure that you are aware of risk factors as well as the possibility of unexpected repair costs will allow your repair to move quickly through our queue and diagnostic process and get back in your hands sooner!