Snagit 3.1. I can't remove the white background of a logo. I tried to take a video using SnagIt; however, it would not let me capture the SnagIt Editor. I tried the help guide. It's a PNG with a white background.
Basically what I did was first to save the image in a format that supports transparency. And you report you are using PNG. So that should be fine.
What you likely need to do next is to configure the background as transparent. To accomplish that, click Image > Canvas Color and choose the checkerboard transparent there. I may not have totally thoroughly read the articles Rick posted, but I did give them a once over before posting here. I'm not sure they mentioned this aspect.
Sometimes I find that transparency won't work until I also close the images, then re-open the one where I'm trying to make it transparent.