I have a mid 2011 i5 mac mini that occasionally freezes up but it is worse when I come in the morning and try to wake it from sleep. The screen is grey andI get the spinning pinwheel and have to manually reboot. Any ideas?
Next is to check what you have left running when it goes to sleep.
Try this: Go to System Preferences>Energy Saver. Set the computer to sleep at never (the slider is moved all the way to the right). Uncheck the put hard disks to sleep and wake for network access. See if that helps.