Update your system regularly via windowsupdate.microsoft.com, and also:
Windows 7 does not wake up from sleep - Super User
Ideas for resolving not coming out of sleep:
1. Look in your BIOS for the suspend ACPI options and try to switch modes among "S1 and S3", "S3" etc.
2. Ensure "Allow this device to wake computer" is checked in in "Device Manager/$device$/ Properties/Power Management", where $device$ stands for keyboard and mouse.
3. Turn off Hybrid sleep, see explanation here (for vista, but is the same)
4. The hibernation file is sometimes disabled by disk cleaning, to restore do in cmd run as administrator "powercfg -h on".
You can use the following command to troubleshoot sleep problems and return...