iMac not going to sleep

[xxfury2xx]

I went into the energy saver options under system preferences and set it up this way:

 

Display Sleep: 15 mins

Computer Sleep: 1 hour

 

The display goes to sleep just fine, but the computer doesn't do it. Anyone else have this issue or know how to fix it?

 

I do have a pair of external speakers plugged into my imac (early 2009), could that stop it from going to sleep?

 

Thanks for any help.