If your camera is supported and setup correctly but dslrBooth can't connect to it or loses the connection after a while, there are a variety of reasons this can happen but here are the likely causes:
USB cable is damaged or low quality. Connect the camera using a high quality usb cable and not an HDMI cable.
The usb cable is too long.
The usb cable is defective.
The usb hub you are using is defective or cannot supply enough power.
The camera power adapter is defective or not supplying enough power. Use genuine Canon/Nikon power supply instead and retry.
The power supply to the camera is interrupted.
Windows turns off power to USB ports after a period of time. See Disable Power management for USB Device and this article.
The USB port on the computer or camera is damaged.
Things to try:
Try a different, shorter usb cable. Preferably the one that came with the camera.
Plug the usb cable directly to the computer and not through a hub.
Try a different usb port.
Replace the camera power adapter.
Close any other photography software such as Adobe Lightroom or Mac Photos.
Put your camera on Manual Mode.
Go to Settings, Camera Settings, change all the settings for both Photo and Video.
Canon
Use a fully charged battery and not a power supply. Some power supplies are known to cause issues.
Close EOS Utility
Turn off Wifi mode if available.
Set the Mode Dial to Manual (M).
Set Live View Shoot. to Enabled.
Set Live View shooting AF mode to Quick mode.
Set live view shooting settings, metering timer to 30 minutes.
If using Rebel XT/350D, 20D or EOS 5D, Set the camera to 'PC Connection' mode.
Nikon
Close Nikon Camera Control as well as other apps that might be connecting to the camera.
If using an older Nikon camera such as the Nikon D40 or earlier, make sure camera setting for USB Mode is PTP.
Windows 10 N Edition
Checkout the following support article if you're using Windows 10 N edition.