Encrypting TI-84 programs I've seen this with other programs, but even as an experienced programmer i can't quite encrypt programs. By that I mean: if i see a list of my programs under the 'execute' menu and then i switch to the 'edit' menu, I find that the program disappears, like it's uneditable or encrypted. Do I need to modify the program on my computer for this? Or is there a special keystroke which can encrypt the program itself on the calculator?

Transferring data and programs to the calculator requires a lot of energy that almost dead batteries cannot provide. Change batteries and try the transfer again using TI Connect. To transfer from a similar calculator the receiving one must be in RCV (receive mode).

No, you'll have to manually type it in. The TI and Casio programming languages are similar but not identical, and the internal representations are completely different. Even if you transferred a program from one to the other, it would only be a meaningless collection of bytes.

Your program is depleting the RAM. You may be creating too many graphics and when you no longer need them, you are not erasing them from inside the program. 24KB is easily used up. It is also possible that some calculations(if you are doing calculations?) are not converging. Recursion can be quite involved and they take too much time.
What can I say? Even a small program badly designed (no reflection on your abilities) may misbehave after a few iterations.

The TI83Plus has the capability to transfer its OS to another handheld device. It is possible that the TI84Plus hardware will accept it. But why downgrade?. Why not resinstall the OS? The latest version 2.55MP is available on the TI website.
You say emphatically that you tried everything and maybe so, but I will ask you: Have tried to connect the calculator to a computer and explored its content with TI connect. You may retrieve some information about its status.
The TI connect software will allow you to transfer a version of the OS even if the calculator appears to refuse to turn ON (screen contrast problem.) If it cannot it will let you know.

Try again.

I just had this problem: shortcut menus used to work, but stopped, with TI Version 2.55 MP. I discovered that running the preloaded app PlySmlt2 (others work, too) and quitting it fixed the problem, but that later running a non-TI app caused the problem again. So the non-TI app may be misbehaving, as suggested in this TI knowledge base article.

Use the memory manager. Press 2ND [MEM] to bring up the memory manager, then 2 7 to bring up the list of programs in memory. Use the arrow keys to move to the one you want to delete, press DEL, then answer Yes to the prompt. Press 2ND [QUIT] to exit the memory manager.

Press the 2nd button, then the plus button, the 7, then 1, then 2. This will reset your calculator.

The comma key on the TI 84 SE is above the 7 key, and it is just left of (, right of x squared, and below SIN. thats where the "," key is. If you're asking something else, please clearify. My understanding is that you don't know where the comma key is. 

I had that same problem.

the blinking black box on my calculator would stay on.
every time I turned on my calculator, it would say 'ram cleared'
if I held down a button for 2 seconds or so, it would finally respond

SOLUTION:
blow really hard into the I/O port. It fixed it for me!

graphing calulators work much like computers. The have RAM space so they can remember what you have done recently and stuff like that. So when it's garbage collecting it means it's trying to find more space. This generally means that you don't have much much ARC or RAM space left. You can see this under your memerory manager. (2nd + enter) then you can reset your calculaor(2nd plus 7 1 2) or you can go to memory manager and unarchive your programs. Fur an example you have TI 84. Most new TI 84 have sientific tools. so if you don't you it take away the archive (*) by pressing enter and then hit DEL. the more RAM space and ARC space should make it so it doens't garababe collect. Hope this works. i can help you more if this doesn't work. GOOD LUCK