Problems with FCPX

Hello. I have used FCPX on a trial period and have now got a full copy.On the trial it all worked well with no problems but now i take video on my Panasonic sd 900 which records in AVCHD. I have converted files to quicktime.mov and have had little or no response on the FCPX software. The files in the events library once opened have no picture and when i play them to start editing them i get a no response message and if i get any response it comes up with the video has dropped out box as the footage is completely juddery. I have done the proxy setting in preferences but no change. I know this is possibly basic stuff but your expert opinion would be really helpful.