Difficult to finish work started at a previous lab I finished my master's degree last year, and took a PhD position in a different country. I have several ongoing projects/papers from the previous lab but it is difficult to finish them. The reasons are


I am not allowed to spend any time on the previous projects at my new lab
The co-authors from the previous lab are not actively contributing anymore
Some co-authors choose to ignore my emails or respond slowly 
The previous PIs are interested to get the projects finished but do not do much else than ask why things are not already done


The thing is, after working 8-10 hours at my current lab, I am too exhausted in the evenings to do much. Or during the weekends.

I would be quite depressed if the projects get never finished but I am running out of ideas. What should I do?
Working on projects when you are away is difficult in most situations, especially yours. Two possible options to finish them include: 


Adjusting to your PhD workload until you are no longer overwhelmed. When you're at that stage, you can try spending several hours a week on those old projects of yours. This may require saying "no" to some additional projects or opportunities at your new place - at least for the time being.
If possible, taking some time off to go back to your former university. Physical presence will greatly accelerate things, and you won't have to rely on the email so much. Plus, you won't be distracted by all the other things you need to do.


Finally, you can try talking to your old advisor and admitting these difficulties. The two of you may then decide to let it go or figure out a solution together. 

Remember, though: right now, it is essential that your PhD work goes well, since it is key to your future career. Everything else can wait. It's annoying when things don't get finished, but this might be a sacrifice you have to make - at least for the time being.