I have a OS X 10.6.8 on an old macbook pro. I'm not sure if this problem started after I did an OnyX cleanup. If I'm away from the computer for a long time, instead of just going into sleep, it almost shuts down, the screen saver is there, but all previously open applications are closed, and it's starting up when I wake it up. I don't know what that is or why it happens, as it's not in any of the energy saving setups (copmuter is set to never go on sleep).
You are posting in the wrong forum, this is the forum for Intel based iMacs. I suspect if you posted in the MBP forum you may find what you need. The process for resetting MBP's SMC is totally different than on an iMac. Here are instructions for an Intel based MBP: