Q: my Mac is stuck on preparing to empty the trash stopping

It sounds like an incomplete download. A restart will usually take care of that.

If you can use Safari, go to the downloads window and delete all DLs.

If that doesn't work launch Activity Monitor in /Utilities folder.

Quit or force-quit Finder.

If you have no other options hold the power button until your Mac shuts down.

Good day,

I was on this very issue today and also, working on removing some large files from Time Machine so from the geniuses the trick is to //* press the command Key while you are emptying the trash /// so I tried  and it worked for me i am running 10.10.5

have a good day,

captbullett

Apple developer 

link to the help I used :

https://support.apple./en-us/HT201583

Good day,

I have some more info on this if the "Empty Trash stops during this processes just press the command key again until it starts to empty again.

One, will find this is very easy to do and if one remembers this you will never have to call Apple care on a stuck trash bin again

Brian