Computer won't wake up

I have a 5 year old HP Pavilion p6733w desktop running Windows 7. I recently restored it to factory settings to get rid of a bunch of junk files.
The tower doesn't always go into sleep mode and when I manually put it in sleep mode, it will wake up on its own. The issue is that when that happens, jiggling the mouse or hitting a key will not bring anything up. The monitor stays off and I can hear the fans running in the tower but nothing happens. I tried just pressing the power button briefly and that doesn't work. I have to turn off my computer each time this happens. I do have the keyboard set to wake up the computer and I turned off the hybrid sleep and hibernation. The monitor cords are secure.
Please let me know if you need any more info. Thanks.