Mac Goes to sleep after "Start up"

[FSMBP]

I have it that my Mac automatically starts up everyday at 8:30AM. Over the past two days I noticed that right after start up, it goes to sleep.

My Mac is not set to sleep ever. What's the deal?

 

[eawmp1]

It does what I do - hit the snooze button, roll over and go back to slee.

Shut down manually. Then start. Does it sleep then?
Do a restart. Does it sleep then?

 

[spinnerlys]

Have you tried resetting the SMC?
http://support.apple.com/kb/HT1411

 

[FSMBP]

Thanks guys. Well I restarted it manually, and it did the same thing. My Mac is in clamshell mode, hooked up to an external, and after the start up "dong" the Apple logo (on the top of my Mac) starts to glow...weird.

I'm going to reset my SMC, but the article on Apple's site doesn't list instructions for Pre-2008 MacBook Pros. Should I still follow the same instructions?