There is several ways to reset the Ti-89 Titanium calculator. Other than the one shown to you by K24674, just hit [2nd] [MEM] [F1] instead of [diamond] [MEM] [F1], then:
Press [1:RAM] then select [1: All RAM] or [2: Defaults] and [ENTER] to reset the RAM.
Since you didn't give him four thumbs up because, he did what you stated. I'll tell you other ways to do a reset. The reason is because, you may have a locked up calculator that seems impossible to reset.
Push [2nd] [MEM] then [F1]  [ENTER] for yes to reset everything.
If your have downloaded 3rd party shells, games and programs and your calculator is locked up, you may need to take out all the batteries including the small circular one for about 4 hours or more.
If this doesn't work you will have to deal with it, possibly by deleting out what you can to free the calculator up to start operating properly, and re-installing the OS software.
Actually most people don't even need to reset their calculator memory. It is usually just a single variable
that their using that is what hanging them up. Just execute the NewProb
command to delete all single variables
in the folder that your working in by pushing [2nd] [F1]  [ENTER]. This only deletes single variables
a to z. This method is unlikely to miss you up with other programs, functions that are not archived or can be mistakenly deleted on your calculator. Works real good while working out of the main folder. Hope this helps you!