I had that problem too deary!
What solved it was the following precautions I took, and I hope this helps you! ^^
- Make sure no other windows are open of any kind
- Do not click it to open it, but, right click it and choose open
- If problems still occur, force quit it, restart and do the exact same procedure.
- If it /still/ doesn't open with these steps, uninstall it and everything inside the folders, you must empty the trash as well to fully rid it! When you redoes load it, make sure that before hand you had everything you once had at the ready to just put into the following folders you wanted. (Ex: presets, markings, items are to be downloaded so they are in the download folder so you don't have to hunt them down all for just the one purpose in selected trials.)
- Fix the particles so it doesn't have as much lag, since lag can be a problem for opening as well ^^
- If problems still occur After all this, contact a moderator for assistance. Pick an active one to message! ^^ Hope this helped you
Your welcome! ^^
Glad it's working again c: