Tried deleting the preferences?
If that doesn't work you could try moving all Xtensions to the disabled folder then having another go - if that works then it's possibly a corrupt/incompatible Xtension.
Lastly I've had occasions when a specific font causes an instant crash. The solution there is to clear out the font caches.
Information about your OS will help so I (or someone else) can give you more specific instructions if you need them.
Good luck,
Greg