As a new starting point
there may be, depending on your system, various options in the BIOS as to the actual mode used to go into sleep, (S1,S2,S3, Etc.).
You may want to try adjusting these if possible. Also, the motherboard drivers
, have an effect on this, you may wish to check if there are newer versions than the ones you are using.
You could also check for possible upgrades for the BIOS itself, as a few manufacturers were caught out with changes under the skin in Windows 7
Sorry I don't have a one click answer but hopefully this may lead you to a solution