Adding peripherals, installing software, and performing other upgrades can sometimes cause problems with your Mac. Follow these simple steps to stop problems before they start.
Read the documentation.
Many times the documentation accompanying hardware and software contains key information on compatibility or potential problems. I recently added a specific device to my Mac and subsequently experienced frequent crashes. Buried in the middle of the lengthy PDF documentation on the install CD was a statement indicating that frequent crashes may occur if this particular Windows/Mac-compatible device is installed on a Mac! So onto my PC it went....

Know your system specifications and upgrade options.
Click on Apple Menu - Apple System Profiler or Apple Menu - About this Mac - More Info for a hardware and software overview of your Mac. Visit AppleCare Service and Support Website for documentation, specifications, upgrade options, and troubleshooting for your specific Mac model.

Retrace your steps and fix or undo what you just did.
For peripherals or other hardware, make sure the items are firmly attached and properly seated. Remove or uninstall the peripheral or software and see if your Mac operates normally. You may wish to attach the device to another Mac (if you have the luxury of doing so) to see if the device itself is faulty.