On some computer configurations the 3D plan of Architect 3D may freeze while trying to walk around or display only solid colour with no preview. This is caused by out-dated driver software for the video card.
In such case, please initially close all running programs and run Windows Update and install all pending updates found for this system then restart the computer to apply changes. After Windows boots up run Windows Update again to check for updates again - apply if any are found and restart the system again to apply new changes. This should help the computer to update video driver software.
Alternatively, visit the video card manufacturer's website to download and install the latest driver software available for this particular computer system. Restart the computer to apply changes and continue working with Architect 3D normally.