Keys do not respond as they should 3 WILL not display alphabetic if not in t9

Besides the fact that you should get rid of that ancient device as they make life difficult lol you have to change the settings from t9.
When you are in the texting area you only have to hit the right key to change from t9 to Alphabet (not sure it's the exact spelling for t9 but one of the keys (usually bottom left or top left corner will allow you to type normal or to guess words by what you type, some of which can be confusing.)
for the letter e you have to push the 2 key 3 times I believe, if you keep pressing each key you will see different letters, numbers and symbols, perhaps a Users manual is available online (can google it, is available to tell you how to change the texting type.
Dunno this helps but it's so old I cant recall exact details but that's the gist of it.

This happens when you have the Num Lk (Number Lock) key on and you have Pressed the FN Function key at the lower left hand portion of the keyboard. When this happens if you press the keys such as UIOJKLM you will key the numbers 4561230.

Turn your Num Lk off by pressing that key at the top of the keyboard.

If your phone only has the numeric pad you can change the setting from "abc" to "T9". T9 is a predictive texting mode, so if you wanted to type the word "hello" you would just press the corresponding numbers 1 time, for example: 4(gHi)-3(dEf)-5 (jkL)-5(jkL)-6(mnO), so you would only hit 4-3-5-5-6, if the word is not the first word displayed you can hit the next key which is usually either * or # depending on your phone. The T9 setting is usually changed by again hitting either the * or # key, or sometimes 0. It is also sometimes selected on the texting menu from within the message.
Learn how to use T9

You need to press the number key # briefly to switch between the abc, Abc, ABC, T9 abc, T9 Abc , T9 ABC and 123. The Status indicator in the top of line display. If you press and hold all input modes will be displayed.

Either in T9 or Alphabet mode, use the * (asterisk) key. You'll be offered 3 options: caps lock (AB), initial capital (Ab), and lower case (ab). For further details, take a look at pages #50 and #52v of its user guide, which you can download from this location.
Please, let me know if I can help you any further.
Regards, Carlos

Here's how:

Enter text
When entering text, you can change the text input
mode:
• Press and hold [ ] to switch between T9 and
ABC modes.
• Press [ ] to change case or switch to Number
mode.
• Press and hold [ ] to switch to Symbol mode.
Enter text in one of the following modes:
Mode Function
ABC
Press the appropriate alphanumeric key until
the character you want appears on the
display.
T9
1. Press the appropriate alphanumeric
keys to enter an entire word.
2. When the word displays correctly, press
[ ] to insert a space. If the correct word
does not display, select an alternate
word from the list that appears.
Number Press the appropriate alphanumeric key to
enter a number.
Symbol Press the appropriate alphanumeric key to
select a symbol.

Here is a link for a free online user's manual for your convenience:

http://downloadcenter.samsung.com/content/UM/200904/20090420115654593/CMS_-_Samsung_B2100_UM_EU_Eng_FINAL_Rev.1.1_090326.pdf

Please leave us 4 thumbs up :)

You must disable your Predictive text option, T9® predictive text mode allows you to type words with only one keystroke per letter, and the phone interprets what word you want. For example, to type the, press 8, 4, 3. To enable/disable T9® predictive text mode, select Options. Scroll to and select Prediction on or off.

hold a-b button and menu buttom simultaniously

Using T9 mode
T9 is a predictive text input mode that allows you to
key in any character using single keystrokes.
Entering a word in T9 mode
1. Press [2] to [9] to start entering a word. Press
each key once for each letter.
For example, press [4], [3], [5], [5], and [6] to
enter HELLO in T9 mode.
T9 predicts the word that you are typing, and it
may change with each key that you press.
2. Enter the whole word before editing or deleting
characters.
3. When the word displays correctly, go to step 4.
Otherwise, press [0] to display alternative word
choices for the keys that you have pressed.
For example, OF and ME use [6] and [3].
4. Press [ ] to insert a space and enter the next
word.
Other T9 mode operations
• Press [1] to enter periods or apostrophes
automatically.
• Press [ ] to change case. Lower case (No
indicator), Initial capital ( ), and Capital lock ( )
are available.
• Press [ ] to insert a space.
• Press the Navigation keys to move the cursor.
• Press [C] to delete characters one by one. Press
and hold [C] to clear the display.
Adding a new word to the T9 dictionary
This feature may not be available for some languages.
1. Enter the word that you want to add.
2. Press [0] to display alternative words for your key
presses. When there are no more alternative
words, Spell displays on the bottom line.
3. Press <Spell>.
4. Enter the word you want using ABC mode and
press <OK>.



"The faulty interface lies between the chair and the keyboard"

Is it possible someone may have sprayed cleaner directly onto the keypad area?

This causes moisture to get into the keypad and sometimes onto the control board.

This could mean that they control panel frame with keypad (membrane switch) would need to be replaced.

Can you give more details on the cleaning?