Can't wake from sleep(?)

I just installed a new HDD & Win7 Ultimate 64-bit on my friend's PC. Works great except I can't wake it once it goes to sleep. Hibernate is turned-off (it was set like this by default(?).
I saw some posts that this has been an issue, but couldn't find a resolution.

Please help.

My Windows 7 has a setting for sleeping also, not just hibernation. Make sure those settings are set correctly also. In screen saver window, click on the words at the bottom that say: Change power settings. On the left hand pane, there is a "change when computer sleeps" option. Click that, then you can change to never sleep.