I'm glad the memory problem is gone
Now about the other issues...
I know you have several user accounts on the machine, if you have one with Administrator privileges I would like you to logon with that one and try to change the screen resolution, restart the computer and logon again using the same account. Does the resolution stays?
Ahhh guest account can make temporary changes to their resolution but when rebooted everything changes back to default settings. Good one Sleepydude.