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:

• OS X
  • ~/Library/Logs/Unity/
• Windows XP
  • C:\Documents and Settings\(current user)\Local Settings\temp\UnityWebPlayer\log
• Vista/Windows 7
  • C:\Users\(current user)\AppData\Local\Temp\Low\UnityWebPlayer\log

1. Try starting Unity and immediately after double clicking the icon, press and hold Alt on your keyboard. This will start the "New Project Wizard" from where you can start a new project. By default, Unity opens the last project you've worked on, but there was a problem with this project, it might prevent Unity from opening. This is where you can use the Alt+DbClick method.

2. If this still does not help you, and you are on a windows box, you should check your DEP-settings. DEP is short for Data Execution Prevention (How to handle DEP in Windows Vista and in Windows 7) and, as the name implies, might prevent an application from running properly.

3. If you are running windows, this may be an issue with your drivers. Fire up DXDIAG (Start > Run > "DXDIAG") Some users have reported issues with DXDIAG hanging when it gets to Input. Uninstalling the HID drivers has helped resolve this issue for some users

4. In rare cases where Unity cannot start at all, Unity can be run in "compatibility mode" on Windows.

5. If you are still stuck, please contact Unity Support: support@unity3d.com or report a bug.

I found when I get into a startup crash loop that deleting everything in the Library -> ScriptAssemblies folder and letting unity rebuild them on startup fixes the issue

sudo apt-get install gnome

Install Gnome and enjoy. I did the same :)

I had to revert to an old working version, then update little by little WHILE Unity was open. He could process all the assets and everything turned alright.