How do i play whats on the memory card nothing plays video only audio. or what do i need to convert it

First, make sure you have it on CARD (and not DISK), and on the "playback" (and not record) mode. Next, does the camera play back other video clips normally, but just not a specific clip ?
Does the selected video clip frame (index) shown on the LCD screen have a picture ? If not, i.e. it is blank (dark), then it is likely that no video was recorded (i.e. just the audio) when you were shooting that video clip.
If there is a picture (of the video clip frame index on the LCD screen) and only audio is playing, try downloading the clip (from the SD card) to your computer, or simply try to play the video on the SD card (inserted directly into your SD card reader on your computer, or via a USB SD card reader) and see if the video clip will play normally on your computer.