By default, Unity always loads up the last project that you edited, but you can override this by holding down "Alt" while unity starts. Press and hold it quickly after launching unity, and you'll get an option to select a different project or start a new project.
If the problem is with the project, then this will help make unity usable for you again, although it doesn't much help find out what the actual problem is.
For that, try looking at the Editor.log file after unity crashes which can be found here:
answered Jan 13 '10 at 04:05 PM
I've found the solution to my crash-problem. It had nothing to do with the update to a new version or incompatibilities with older versions!
Actually (with the very quick help of the support), it turned out that Unity is not compatible with some settings of Airfoil (a program that I use for sending music from my PC to remote speakers).
After uninstalling Airfoil, everything went back to normal.
Wow - I would have never thought of that... BIG thanks to the Unity support! <3
answered Feb 14 '11 at 01:47 PM
In case any Mac OS users land here with the same problem, i.e., "Unity crashes immediately on startup", please try the following.
It requires the root password.
From the terminal:
If it says it requires read and write permissions, allow it. It will then go on to import the bootcamp assets and start Unity without crashing.
If not, please contact firstname.lastname@example.org
answered Apr 09 '11 at 02:21 AM
The reason for crashing is probably a problem with the currently active scene (the one Unity will automatically reopen when Unity loads your project). Rename the scene file before starting Unity will open the project but with an empty scene.
Possibly the scene is beyond repair (until there's a bugfix for Unity that makes the scene stop crashing) but at least the rest of your project is workable again. You can now try reimport all assets (menu) save the project and reopen the offending scene if maybe problem is fixed automagically.
answered Jan 13 '10 at 10:35 PM