Yes, I'm also thinking along the lines of too much sugar and that it's probably reached it's alcohol tolerance.
So, with a bit of maths, work out how much water goes with 2kg of sugar (allowing it to be 6kg per 21 litres of water), so that would normally be 7litres to 2 kg - hence you'd need to be able to add a further 7litres - if that doesn't work i.e. it doesn't re-start with just the extra dilution, then you'll probably need to add a champagne yeast and some nutrients - but you'd need to look up on one of the wine making websites about restarting stuck fermentations and follow the instructions.
It usually entails some water and some of the stuck ferment in a fermenter of some sort, add the yeast/nutrient, let it get bubbling, add more of the stuckie, let that get going, add more, etc etc until you've got something like between 1/3 and 1/2 of the stuckie refermenting. then you should be able to add the rest and airlock it from there and treat it as normal.
Of course, if you'd taken a gravity reading at the start, you'd know what the %ABV is i.e. starting gravity, minus gravity of stuck ferment, gives you the drop in gravity numbers and say for arguments sake it's a drop of 100 points, then you'd have a ferment of about 13.5% ABV.
you can also distill with sugar left to ferment, but if you chose that route, I'd make sure that you only put 3 litres in the still not 4 and that you made sure that you use a cap full of distillers conditioner into each new charge of the still - oh and run it well away from where pets/kids/other family members are likely to pass, then if it does over boil and "burp", there'll be no harm done (or injuries)
Don't throw it away though, have a go at sorting it out, as it's a waste to bin and it's also part of the learning curve......
What the large print giveth, the small print taketh away. Tom Waits.
