AdiIRC

It's not safe to address your code, because what we see is almost certainly not what you posted. I don't see the equals in your if statement, and there might be other things. To make sure your code displays correctly, click on the PRE button for the symbols to surround your pasted code. Then before posting, click on PREVIEW to make sure your post looks right.

When someone comes online:
on *:NOTIFY:{
if ($nick Zedd) /splay -q C:\Users\Lenovo\Desktop\yabadabado.wav
else if ($nick David) /splay -q C:\Users\Lenovo\Desktop\attention.wav

When someone goes offline:
on *:UNOTIFY:{
if ($nick Zedd) /splay C:\Users\Lenovo\Desktop\234526__foolboymedia__announcement-end.wav
else if ($nick David) /splay C:\Users\Lenovo\Desktop\234526__foolboymedia__announcement-end.wav

So I noticed that it doesn't play a notify sound (when a user comes online, or goes offline ) ONLY when there is more than one user online

Ah, so the problem is not due to the forum hiding characters, they're actually missing from your code.
There's 2 main types of if statements, either boolean or comparison using an operator. What you're doing is not using an operator, which is having the effect of a boolean statement with is true except when the string is something like $null or 0 or $false. So it looks like your code is always true, because you have a non-zero string inside the if statement. What you really want is something like

if ($nick Zedd) command goes here

First thing you want to do when something "isn't working", is to investigate the problem. Try including an echo to the status window as the first command of the :EVENT: handler, to see whether the problem is that the event is or isn't being triggered, or whether there's a problem with your branching logic, or a problem with the command that's supposed to be performed. Have something like:

echo s debug: $scriptline $nopath($script) event $event nick $nick (1) ($1-)

Your usage of a debug message will differ in some situations, where you need to include contents of variables, etc.
If you want to verify which branch is taken at an if statement, you can include the message as part of the commmand.

instead of

if ($nick zedd) splay filename.wav

have it do:

if ($nick == zedd) { echo -s debug $scriptline $nopath($script) | splay filename.wav }

It's important to have something in the debug message that identifies where it's coming from, because otherwise you run the risk of getting spammed by debug messages several months down the line which you have no idea which script is putting them there

Nothing seems to work.

Every time you give me a new line, a new code, and there's always an error or something wrong

I was the one who gave you the original code at https://dev.adiirc.com/boards/1/topics/1769?r=1790#message-1790 if you compare to what you have posted here, it is missing various things.

Your code should look like this:

on *:NOTIFY:{
  if ($nick == Zedd) /splay -q C:\Users\Lenovo\Desktop\yabadabado.wav
  else if ($nick == David) /splay -q C:\Users\Lenovo\Desktop\attention.wav
}

on *:UNOTIFY:{
  if ($nick == Zedd) /splay -q C:\Users\Lenovo\Desktop\234526__foolboymedia__announcement-end.wav
  else if ($nick == David) /splay -q C:\Users\Lenovo\Desktop\234526__foolboymedia__announcement-end.wav
}

That's exactly how it looks. And it's not working at all.

All it does is gives me a notify when I connect that all my contacts are offline, even if some of them are online

I think you should look closer, you'll see there was -q missing in the UNOTIFY events etc, try copy/paste my code and replace yours, then try again.

Also make sure you don't have sounds set for these nicks in the Notify options to avoid overlap.

So I added 3 nicknames to my notify list, and I noticed the following:

I only get a notify message and sound for the second nickname who is online. But no message or sound when the first nickname in the script and the last nickname are online

Which takes us back to my very first question. Why doesn't it work when there's more than one nickname online??

Open your config.ini file then copy/paste the [Notify] section here, also on what network are these users so I can test?

Also if possible, upload the sound files, I think they can be attached here.

on *:NOTIFY:{
  if ($nick == Xavi) /splay -q C:\Users\Lenovo\Desktop\yabadabado.wav
  else if ($nick == Laila) /splay -q C:\Users\Lenovo\Desktop\attention.wav
  else if ($nick == Bam) /splay -q C:\Users\Lenovo\Desktop\peekaboo.wav
}

irc.librairc.net

Now it notifies me for the second and third nicknames. But gives me nothing for the first nick

I need the [Notify] section from your config.ini file and your sound files to recreate your setup.

Here are the sounds.

How to access the notify section or config.ini?

You can type in the Editbox: //run $adiircdir

The config.ini file should be there.

What do I do exactly when I open options - editbox?

Because I get no results when I search for //run $adiircdir

And as I mentioned, now it gives me a notification for the 2nd and 3rd nicknames. But no message or sound for the first nick Xavi

Editbox is where you type text.

[Notify]
n0=Xavi¦irc.librairc.net¦¦0¦C:\Users\Lenovo\Desktop\yabadabado.wav¦0¦C:\Users\Lenovo\Desktop\234526__foolboymedia__announcement-end.wav¦False¦False
n1=Laila¦irc.icqchat.net¦¦0¦C:\Users\Lenovo\Desktop\attention.wav¦0¦C:\Users\Lenovo\Desktop\234526__foolboymedia__announcement-end.wav¦False¦False
n2=Bam¦irc.icqchat.net¦¦0¦C:\Users\Lenovo\Desktop\peekaboo.wav¦0¦C:\Users\Lenovo\Desktop\234526__foolboymedia__announcement-end.wav¦False¦False

You should remove the sounds from the Notify options as I mentioned earlier, this is one of the causes for the confusion.

I figured out the other issue, it wont trigger on NOTIFY/UNOTIFY if adiirc is the focused window, should be fixed in next beta.

I set it to NO SOUND in the notify options. And by the way, if it was on, it wouldn't cause any problems. But it would play the notify sound twice.

Now there's another issue. If I add a 4th nickname, it wouldn't notify me through a message or a sound.

Next beta? Sure! If I'm still alive

What exactly do you mean by "Next beta? Sure! If I'm still alive" ?