I'm using a TI-84+
1. If I hit [2nd] then [mem] it does nothing. Both keys work for all other functions. This has never worked for me, but I was always able to work around it.
2. Until now; for some reason when I try to graph anything lately it gives me ERR: UNDEFINED. Even simple functions like y=x. I figure a reset would fix this, but I can't reset because of #1.
UPDATE: Fixed #2.
UPDATE: Fixed #1
One of the Mirage settings is to "block access to the memory menu", and somehow this got checked. If you don't have Mirage it won't be a problem.
Also, you can clear the RAM by creating an assembly program. Name it whatever and then open the catalog, select "Asmprgm", then add "18FE". Then go back to the homescreen and type Asm(whatever) and hit enter. And then take out a battery and put it back. A message pops up that says "RAM cleared."