Ordinarally, the RPi uses an SD card for memory storage. Those cards have gained a reputation for unreliability. My suspicion is oxidation of the contacts.
The RPi is now capable of USB drive storage. I setup an SD card and an SSD hard drive with the RPI operating system. I followed the instructions for use of a USB memory device and now use a 250Gb SSD for memory storage and operating system installation. The SSD is much faster than an SD card and has enough space to contain the operating system and any programs I wish to install.
