problems with matroska (.mkv) playback

Hi I'm having trouble playing .mkv high def files. I started out trying to convert them to .mp4 for playing on the ps3 but run into troubles and discovered that I can't even play them back properly. I've used three players, vlc, totem and MPlayer. vlc and totem play back but only show snipits of frames, MPlayer plays audio fine but no video at all, here are the error messages:
vlc:
[00000304] mkv demuxer error: cannot load cues (broken seekhead or file)
[00000339] a52 decoder: A/52 channels:6 samplerate:48000 bitrate:640000
[00000346] pulse audio output error: Failed to connect to server: Connection refused
[00000346] pulse audio output error: Pulse initialization failed
[00000307] ffmpeg decoder error: more than 5 seconds of late video -> dropping frame (computer too slow ?)
[00000307] ffmpeg decoder error: more than 5 seconds of late video -> dropping frame (computer too slow ?)
[00000283] main playlist: stopping playback
ben@the-bishop:~$ vlc
VLC media player 0.8.6e Janus
[00000304] mkv demuxer error: cannot load cues (broken seekhead or file)
[00000339] a52 decoder: A/52 channels:6 samplerate:48000 bitrate:640000
[00000346] pulse audio output error: Failed to connect to server: Connection refused
[00000346] pulse audio output error: Pulse initialization failed
[00000307] ffmpeg decoder error: more than 5 seconds of late video -> dropping frame (computer too slow ?)

Totem:
[00000304] mkv demuxer error: cannot load cues (broken seekhead or file)
[00000339] a52 decoder: A/52 channels:6 samplerate:48000 bitrate:640000
[00000346] pulse audio output error: Failed to connect to server: Connection refused
[00000346] pulse audio output error: Pulse initialization failed
[00000307] ffmpeg decoder error: more than 5 seconds of late video -> dropping frame (computer too slow ?)
[00000307] ffmpeg decoder error: more than 5 seconds of late video -> dropping frame (computer too slow ?)
[00000283] main playlist: stopping playback
ben@the-bishop:~$ vlc
VLC media player 0.8.6e Janus
[00000304] mkv demuxer error: cannot load cues (broken seekhead or file)
[00000339] a52 decoder: A/52 channels:6 samplerate:48000 bitrate:640000
[00000346] pulse audio output error: Failed to connect to server: Connection refused
[00000346] pulse audio output error: Pulse initialization failed
[00000307] ffmpeg decoder error: more than 5 seconds of late video -> dropping frame (computer too slow ?)

MPlayer:
Playing /media/disk/videofile.mkv.
[mkv] Track ID 1: audio (A_AC3), -aid 0, -alang und
[mkv] Track ID 2: video (V_MPEG4/ISO/AVC), -vid 0
[mkv] Will play video track 2.
Matroska file format detected.
VIDEO: [avc1] 1280x720 24bpp 23.976 fps 0.0 kbps ( 0.0 kbyte/s)
xscreensaver_disable: Could not find XScreenSaver window.
GNOME screensaver disabled
[VO_XV] It seems there is no Xvideo support for your video card available.
[VO_XV] Run 'xvinfo' to verify its Xv support and read
[VO_XV] DOCS/HTML/en/video.html#xv!
[VO_XV] See 'mplayer -vo help' for other (non-xv) video out drivers.
[VO_XV] Try -vo x11.
Error opening/initializing the selected video_out (-vo) device.
==========================================================================
Forced audio codec: mad
Opening audio decoder: [liba52] AC3 decoding with liba52
Using SSE optimized IMDCT transform
Using MMX optimized resampler
AUDIO: 48000 Hz, 2 ch, s16le, 448.0 kbit/29.17% (ratio: 56000->192000)
Selected audio codec: [a52] afm: liba52 (AC3-liba52)
==========================================================================
AO: [pulse] Failed to connect to server: Connection refused
AO: [alsa] 48000Hz 2ch s16le (2 bytes per sample)
Video: no video
Starting playback...
No bind found for key ''.
A: 59.8 (59.8) of 2621.8 (43:41.7) 1.6%

other media files work fine. any help would be greatly appreciated
thankyou
ben