Windows 10 comes with some of the UWP apps installed. These are apps that you’ll need for day-to-day computing. Camera app is one of these pre-installed apps. If your device is equipped with a webcam, you can use Camera app to capture yourself. In case if you uninstalled Camera app earlier, you can download it back from Microsoft Store.
However, there is a possibility that sometimes Camera app couldn’t connect to hardware or other resources it would need. In such condition, it would failed to start camera. See the screenshot below.
Can’t start your camera
If you’re sure that the camera is connected and installed properly, try checking for updated drivers. If you need it, here’s the error code: 0xA00F429F <WindowShowFailed> (0x887A0004).

So if you’re also facing this problem and can’t start camera in Windows 10, refer below mentioned suggestions to fix it.
Fix: Can’t Start Camera In Windows 10
Fix 1: General Suggestions
1. Restart your system.
2. Open Device Manager, go to Camera section and right click on your camera device, select Uninstall. Click Action > Scan for hardware changes. Check if issue is resolved, else continue to step 3.
3. In Device Manager, right click on Camera device, select Update driver. Follow on-screen instructions.
4. If step 3 doesn’t works, go to your device manufacturer’s website and install latest webcam drivers for your system model.
5. Reinstall, if you’ve external camera.
6. Go to Settings > Privacy > Camera, make sure the Camera access for this device option is On.

If you continue facing this issue even after trying above suggestions, refer FIX 2 below.
Fix 2: Using Registry
1. Open the Registry Editor by running regedit.exe command.
2. Go to HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Windows Media Foundation\Platform.
3. In right pane of Platform registry key, create new registry DWORD (REG_DWORD). named EnableFrameServerMode.
4. Let the Value data of EnableFrameServerMode registry DWORD remain set to 0, as you created it.
5. Close Registry Editor and restart your computer.
After rebooting your machine, the issue should be resolved.
Hope this helps!
Related: We Can’t Find Your Camera (0xA00F4244) In Windows 10.