The basic MIDI part of the way Sonar works is pretty much the way it's been for a long, long time, back when it was called Cakewalk whatever. It's the same piano roll thing, event list, etc. The most that has changed over the years is the audio stuff (non-MIDI waveform stuff, same as recording on tape), but if you just make MIDI tracks and record / play, plus use the piano roll, it should be the same as before.
But the you need to have MIDI ability in your computer. Getting sound from youtube is all audio, not MIDI. Since it's not the same thing, playing those clips doesn't show that your current computer can do MIDI.
Did you have an old Soundblaster card in your computer 10 years ago or some other sound card that had MIDI capability? Even if you didn't use the inputs and outputs to work with an external keyboard, you could still use a MIDI program like Cakewalk to play the sounds on the sound card itself (they often have General MIDI synthesizers right on the card, a synth on a chip).
Realtek is usually the onboard audio that most computer systems come with built in these days, but that's MIDI. It could be that you didn't have to deal with any of this before if you bought a computer with a sound card installed that had MIDI, but most computers don't come with sound cards at all in them anymore, because it's all onboard (on the motherboard), at least the audio part is.
Resolution: so if my guess are correct, then you have to buy a sound card -- one with MIDI capability, then install it in your computer or have it installed. Then you may have to get into the Sonar preferences dialog to select the new soundcard (if it doesn't automatically recognize it).
BUT DOUBLE-CHECK first to see if you already have something MIDI in your machine: Run Sonar, bring up the
Preferences dialog from the
Edit menu, scroll down to the
MIDI section and select
Devices. Is anything listed there?
If there's nothing in that box, ask here about what sound cards you need. I see some for about $40 online, but I'm not familiar with recent sound cards.
Speck