Definitely more information is going to be needed. A spinning beach ball typically means a process is either stalled or extremely slow, tying up all system resources or blocking other activity. Knowing when it occurs with regards to the normal boot up process would help. Example, from your brief question, I'm guessing the gray Apple icon appears with the spin wheel below it and goes away. After that, you should see a (typically) blue screen as the finder loads, then your desktop, then your menubar items, then your desktop and dock items, and finally whatever apps you may have set to launch at logon. You can eliminate the logon items by holding down the shift key at startup. If the system boots normally in "Safe Mode" then you're probably looking at a login item or possibly a bad 3rd party driver.
Let us know... the more detail the better.