Error previewing video

Created my first disc successfully the other day, then downloaded video editing software which removed Quicktime & Real Player, not bothered as I did not use them, did not like the editing software so uninstalled then system restore.
Both players had not returned but now when I try to preview a video using dvd builder it says 'error starting the clip'
Can play all vids on my PC, think this editing software has removed something that dvd builder needs but do not know what, any ideas please, am really stuck. Thanks