Did you backup your project file? It hasn't happened yet, but a problem of this kind can lead to a corrupted project file. Back it up and date-/time-stamp it before anything more goes wrong.
After that, first thing I'd try is to disconnect the media without erasing it. Within FCP, press SHIFT-D and choose "Leave Files on Disk". Now reconnect the media. That "flushes" the project-media relationship and can eliminate some problems.
Other than that, there is no easy way to do it other than just to check one file at a time. You say the crashes occur when you render, so just select one file at a time and render it (APPLE-R). If the file renders, save the project file and render the next one until you find the culprit. Remember that FCP see all the parameters of a file (for example, a still image's RGB/CMYK mode), so you may have to go out of FCP to check the source files themselves. If you find the offending file, sometimes a simple open/resave in another application (eg. Adobe Photoshop, QuickTime Player) fixes the problem.
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