OS X macbook sleep

I am running a Macbook. I installed OS X a few days ago.
Since then I am having a problem waking up the mac after it goes to sleep, not always but more often than not.
When I open Mac the grey screen is there, I press a key, which before always woke the Mac up.
Now it will not wake up, I have to power off and power up again and I get the message "you shut down because of a problem".
Other times I try to wake it and there is a small grey box that follows the arrow around blotting out the screen as it goes but I can sometimes type in my password and it will wake up.
Previously never had to enter password to wake up. Is there a setting that has been changed?
dstan

I'd start by deleting the file:
BootDrive > Library > Preferences > SystemConfiguration > com.apple.PowerManagement.plist

To disable password on wake
Apple Menu > System Preferences > Security & Privacy > General > Uncheck Requires password

did all that, problem persists
I can see the windows on the desk top through the dark screen but can not see the arrow to be able to move it around

Seems to be a bit of this going around.

You could make sure all your system updates are done.
And let Apple know.

Thanks Kaveman