Are you saying you leave your pc on when you`re not using it overnight ? OMG How cruel
But seriously, turn it off when you`re not using it JMO.
But, if you try to start the screensaver manually, does it run ?
What time do you have it set to shut off the monitor ? That rarely fails.
Are using a wireless keyboard and mouse ?
If it`s brand new, and not doing everything you want it to, I would take it right back. There is no reason to be unhappy with it.