The white screen is most probably due to low RAM, try to archive some other programs. To do this, press [2ND] + [+] to go to the memory screen, then press , then . This will open a list, programs marked with an asterisk are archived. Press enter to archive/unarchive a program.
About "what buttons do what" in mirageos, [2ND] selects things, [MODE] exits mirageos, and [X,T,θ,n] allows you to edit the properties of a file. Use the graph buttons ([F1] to [F5]) to choose options.