Some people have had difficulty with the Circuit Playground Express on Windows 10 after installing the Arduino IDE and the Arduino Board Support Packages Arduino SAMD and/or Adafruit SAMD. The problem is that these Board Support Packages install unnecessary drivers on Windows 10. This causes two problems:
1. CPLAYBOOT does not appear when double-clicking the reset button on the board.
2. Attempting to upload an Arduino program generates an error like:
An error occurred while uploading the sketch
Unsupported ARM7TDMI architecture
We are working with Arduino to update these packages to fix the problem. In the meantime, the fix is to uninstall the bad drivers. Three unnecessary drivers are installed, one for CPLAYBOOT, one for CIRCUITPY, and one for Arduino programs running on the Circuit Playground Express. You should uninstall all of them.
In all three cases, you open the Device Manager, by right-clicking on the Start menu and choosing Device Manager. Then open the Ports section in the new window. You'll see something like the the listing below. The wording will vary, but it will include "Adafruit Circuit Playground Express".
You want to uninstall the driver for that device. Right-click on the device, choose Uninstall Device, and when the dialog box comes up, check the box that says "Delete the driver software for this device". and click OK. It will look something like this:
You do this three times, following the procedure above each time.
1. First, double-click the reset button, so all the NeoPixels turn green. Normally CPLAYBOOT would appear, but if the incorrect driver is installed, it will not appear. Then unplug and replug in the board.
2. Double-click the reset button again. This time CPLAYBOOT should appear. Upload an Arduino program to the board, such as Blink, following the directions in the Arduino section of this guide.
3. Uninstall when CIRCUITPY is visible as a drive, if you have CircuitPython installed on the board.
Each time you'll see an entry in the Device Manager similar to the above, with slightly different wording, and a different COM port. Uninstall the device as shown above.
If you are pressed for time, number 1. is the most important driver to uninstall.
After you uninstall each device, you can unplug and plug the board in again, and it will reinstall, using a built-in Windows driver, instead of the incorrect one. Double-click the reset button to get CPLAYBOOT and reinstall that as well. The new devices will show up in Device Manager as "USB Serial Device (COMxx)" instead of "Adafruit Circuit Playground", similar to the image below:
If this does not solve the problem of CPLAYBOOT not appearing and the ARM7TDMI error, please post in https://learn.adafruit.com and let us know.