After a reboot, both the internal memory card and the removable card are not present. File Manager doesn't show them in the right pane. The removable card reads fine in my laptop.
LoadApplet shows there is something running in the background always.
I have rebooted several times.
I have completely new to Linux, so if anyone posts instructions, please be extra specific.

Edit: after several reboots, the internal card is back but the removable card is still missing. It doesn't show in File Manager.

Edit again: after several more reboots, the removable card is back. No reason.