How do I get my dyson vaccume cleaner to stand up straight again?

Turn off and unplug the machine. Continue by leaning vacuum on its side, with the blade perpendicular to the ground. Locate the u-bend cover, press the yellow release button, and look for any possible blockages. These blockages may be preventing the machine from locking in its upright position as well as reclining when already locked. See below link for visual guides.