Help with a problem in the Canvas

When I take a video clip or master templates (any moving image ) in the viewer looks perfect , but when I take it to the timeline and reproduce on the canvas . It looks cut , skips several frames and frozen rather than dynamic image stays. The sound is perfectly continuous . I do not know why it happens or know how to solve . Can you help me? Thank you . ( I hope you understand me with my English , I'm Spanish )

Sounds like a simple playback issue.
What format/codec is the original clip?
In the Viewer menu (top right of Viewer), are you set for Better Performance or Better Quality?
Do you have Background Rendering turned on or off?

Most important, what Mac model, how much RAM, and what is your media drive (Firewire, Thunderbolt, USB 2, USB 3)?

It is not the 1st time I use this mac finalcut. It has always served me well and I have not changed anything in the settings. Not only with video, if I use a default by the program also occurs master templates, so it has nothing to do with the type of video.
Of course I have rendering before playback.

Let me make a wild guess: you are storing your media and libraries in the system drive. This can lead to slowdowns, especially as the drive gets fuller. 1) Use a separate drive with a fast connection to your mac (preferrably usb3 or thunderbolt). 2) Always allow a hard drive "room to breathe"; a drive that has less than about 25% free space can slow down considerably - even more if it is the system drive.

Refusing to give requested information makes it next to impossible to help with your problem. If you think the information I asked for is relevant or not, there may be things in that information you're not aware of. Thus, we can only make uneducated guesses. Please give us more information that will help us pinpoint the bottleneck.

As for "breathing room", all hard drives must have enough space for the OS and apps to write temporary working files that we end users never see. The more data on a drive, the more of this temporary working space is needed. Thus, for any and all drives connected to your computer, you need 10-15% of each drive's capacity left as free space (25 is a really high, unnecessary number). When you get below this percentage, your system can exhibit all manner of odd behaviors. Slow performance is only the tip of the iceberg.

So, where is your media, system or secondary drive?
What type of drive it is?
What percentage of each drive is free space?
What codec is your media?
Have you turned off background rendering?
Do you have FCPX set for Better Performance or Better Quality?

Without this information, we can not troubleshoot your system, period.

The codec could in fact be an issue. Just because it worked fine before doesn't tell us anything. It's not working fine now, and we need some necessary information, please.