Most issues can be resolved with very little hand wringing.
When encountering unexpected behavior, there are a couple of very quick tests you can perform to isolate and rule out the more common problems that users encounter.
Now that you've considered whether your problem is more likely to be software- or hardware-related, and FCP- or Mac OSrelated, the next step is to eliminate the obvious with an appropriate quick fix. Often these quick fixes will clear up the problem entirely.
Restart the Application
It's almost too obvious to state, but if indications are pointing to a software problem, the first thing to do is always to restart Final Cut Pro. Simple, quick, and never a bad idea.
Shut Down and Restart the System
The next quick fix is to try shutting everything down, including the computer (use Apple menu > Shut Down) and any connected peripherals, camcorder, or deck. Then start up your computer, followed by your peripherals. Then launch Final Cut Pro.
This allows your machine to reset itself completely. The more complicated the hardware and software in your edit bay is, the more likely that a malfunction can occur. Completely resetting your system brings it back to square one, and often can fix the problem.
Note that in many cases, a full shutdown is required, rather than choosing Restart from the Apple menu.
Create and Log In as a New Admin User
This quick fix involves creating a new admin user to see if the issue is isolated to the user you're currently logged in as.
Although you could go into your home library and remove your preferences to eliminate preferences as the cause of a problem, it's easier to simply log out of your current user and log into a clean user specifically created for the purpose of troubleshooting. When you log in as a new user and run FCP, you can check the same project, media, and hardware using a fresh set of preferences. Don't forget that you will need to move a copy of the project you're testing to the /Users/Shared folder in order to access it using the new user account.
This is the fastest way to rule out several issues at once. Because FCP preferences are stored in the user's folder, problems specifically caused by corrupt or incorrectly set preferences will in all likelihood not exist for other users on the same system. Any special software that exists only in your home folder can be ruled out as well.
If you still see the same behavior, you can safely bet that preferences are not the issue, and you'll have to broaden the scope of your investigation. If on the other hand the problem disappears, then you know that the issue is related to something within your user login. Although that might be preferences, it could also be anything else installed there, such as applications (plug ins, presets, and so on) that you installed only in your user folder, conflicting applications that your user automatically starts at login, and anything else that your user employs that is not shared by other users.
Startup applications are only listed in the Accounts system preference in the Startup Items pane. In some instances, that Startup Items pane may be the only way you would know that an application was running in the background.
After using a new user for testing issues, delete the new user. You should create a brand-new user the next time you need a fresh account for troubleshooting.
FCP Rescue is a good third-party tool developed specifically for manipulating FCP preferences files (http://fcprescue.andersholck.com/).
Remove FireWire, USB, and Other Devices
External devices have the potential for creating conflicts, whether from special drivers required by the device, or simply because the device or device software is not compatible with other devices. This extends to devices you wouldn't normally think of, such as FireWire and USB hubs. Sometimes PCI cards or RAM, and even hard drives, can cause conflicts for one reason or another.
This obviously shouldn't keep you from investing in the products you need to get your job done, but keep the potential device conflicts in mind when you're troubleshooting. One useful quick fix is to remove all devices you are not troubleshooting.
For instance, when troubleshooting an Edit to Tape issue, you only need the deck or camcorder, your project, and the project media (hopefully located on your internal hard drive) to isolate the issue. After you've solved your problem, you can reconnect the other devices you need.