Resetting the PRAM

Commonly know as 'zapping the Pram'

This is usually a good way of solving some of those start up problems.

For instance if your Mac gets stuck in start up mode, all you need to do is hold down the Option (Alt) key plus the P and R keys. The boot chime will sound, wait until it chimes again before releasing the keys.

Depending on your Mac and it's age the key name or symbol may change.