Unfortunately you have not really given us much of a clue about what, exactly, is the problem!
From what you say in your title one might assume this is a problem you are seeing in the upper left corner of the workscreen, the Media pane. If so, top right corner of that pane has four "boxes" in a "square", right-click those boxes and choose "Large icons".
OTOH, if this is when a video is imported to the timeline, check ProgramSettings>Video/Audio>Timeline>Simple video object... is NOT ticked.
If neither of these is the solution please post back with much more detail. This post will show you what we really need to know!