W520 sleep

[liquid93]

I've had my w520 for about 3 weeks now,last night for the first time it started going to sleep every thirty minutes or so.I checked and sleep mode i had set to never,so is the harddrive.I've got everything set to never.It still went to sleep.It is on AC power and no battery connected.I don't mind it going to sleep but I would like to say when,and if ever.Help please