Crashing? Repair Permissions with the Disk Utility. Trash the FCP preferences with FCP Rescue: https://www.pistolerapost2.com/fcprescue
Not playing back at all? There are LOTS of things that cause this. Read the Apple article for a nice big list of things to check:
#12 Dropped frames on capture/playback
Shane’s Stock Answer #12:
https://docs.info.apple.com/article.html?artnum=58640
1) Do not capture to your main system drive. Since it is busy reading the operating system and application files, it will intermittently drop frames during capture.
2) Do not under any circumstances run any anti-virus/filesaver software. Including Norton and Virex. Sure, Apple doles out Virex for free, but FCP doesn’t cooperate with it very well.
If you absolutely feel you must keep Virex installed on your system then use Kevin’s script to shut it off before you use FCP:
https://www.pistolerapost.com/viewing/virexhalt.zip
3) Check the format of the drive you are capturing to. It should be Mas OS Extended, jornalling off. If it isn’t, copy your files from it and re-initialize it. If it is any other format, you will encounter problems. If not at first, then eventually.
4) Trash the FCP preference files. Use FCP Rescue available here:
https://www.pistolerapost2.com/fcprescue
Shane Ross
Alokut Productions
http://www.lfhd.net