Laptop has trouble coming out of hibernation

Hello,

I have just bought this Lenovo laptop this january and it was the worst thing I have ever done. I have been having problems with this computer since day one. The computer recently got restored by the geek squad and now when I leave my computer alone for about 15-20 minutes it will go to sleep or hibernate on its own and when i go to try to open it back up and continue to do what I was doing i get a black screen that says something like computer failed to come out of hibernation. It gives me a reboot option. When it is rebooted my wireless doesnt work and I always have to restart the whole computer for everything to work like normal again. I took it back to the geek squad and they said nothing seems to be wrong with it. All they did was take out the battery and put it back in and said its fixed. The computer still shows with the black screen when left alone for about 20 minutes in time. What can be causing this? Does anyone know what can be going on?