dirt devil vacuum hand furniture vacuum works but not floor vacuum?

I have a dirt devil vacuum cleaner. Standard upright bagless model, sayd jaguar on the filter container if that helps. It is the standard push style vacuum. It has the connectors which you can use to clean furniture and vacuum by hand if you want. The problem is is that I can vacuum by hand. But when I push the vacuum to vacuum the rug, it does not pick up bits on the rug. I emptied the filter container and shook off the filter. What is it that I need to be doing to find why I can’t use it to vacuum the rug? thanks