TIP: if your iPhone crashed, do following

you need to have at least ssh access to your phone (wait after restart a while, use "ping -t IPHONE-IP")
then look in /Library/Logs/CrashReporter/last-crashxxxxxx.plist with vi

you'll see there a lot informations why springboard not works...
if this does not help, save your data under ~/Library and then you need to restore...