[14.04] Cannot get computer to not sleep

I recently set up an old Netbook (Lenovo S10) as a samba file server with Lubuntu 14.04. It is working great, except whenever I don't stream anything from it for a few hours, the computer goes to sleep. The only way to wake it up is to open the lid, whcih is inconvenient because I have it tucked away by my router without easy accesss.

I used the default power management software (Xfce Power Manager), and set everything to never sleep or hibernate either on battery or on AC power. Despite these settings, it still always goes to sleep when left unatended for a few hours.

Is there anything I can do to ensure it stays awake? Is there a better power management software I should install? It would also be nice to have a sleep/wake schedule so it will be off during the day when I am at work. Or would it be possible to wake it up whenever it gets a request from an outside device?

Thanks for any suggestions!