This is obviously not first hand but...
1. It takes very little current to stop your heart, assuming the current actually reaches your heart and doesn't dissipate or bypass it. It is the current that kills, not the voltage.
I am assuming you are talking about the plug side and not anything after the transformer. Humans are very fleshy and make great resistors so depending on a few things the voltage could split between you and your computer (with a lot more current going to your computer) and what resulting current that gets applied to you dissipates or bypasses you (well, the important parts of you).
How likely it would be to kill you would depend on a lot of things but I'd really rather not tell you here because this is readily available on the civil side of the internet if you felt like spending a few minutes reading about it and if you are successful it would lead to incredible amounts of agony. I can't in good conscious say anymore about the way to do it because it is something that could be done very impulsively and will lead to probably more pain and torture than any other method on this site. It's also worth noting that people have fallen onto power lines (much more current) and ended up living.
2. Depending on how exactly you do it, it could be completely pain free (with you still being completely alive) or lead to burns, seizures, total paralysis, and a whole list of other symptoms. I don't think there is data on the percentages because it is so situational but the risks are very high. It is also worth noting that even if you do everything right there (extremely hard to do) there is potential during the ordeal for your heart to not stop, to seize up and then spontaneously restart, or for some random person to perform CPR (or bring an AED to shock you back if you're really unlucky lol).
3. No probably not
4. Your screams of sheer terror and agony will be very loud as your muscles seize up and you burn/ spasm to death in by far one of the most painful and physically unpleasant ways you could possibly choose to go, but otherwise no pretty noiseless