Not all peripherals work after coming out of standby. The following advice assumes that all of your drivers are...
Microsoft digitally signed:
Your keyboard and/or mouse does not work anymore, requiring reset or power off/on.
- Check and/or replace your screen saver if it is OpenGL based. Switch to none and see if it then works.
- Go into boot.ini and remove the /FastDetect parameter and see if standby works.
- Contact the vendor if the driver is not digitally signed and query them about meeting ACPI.