I had this Dell that did that. It turned out the owner had run a registry cleaner and crippled the machine. We reinstalled the OS and Dell handed out some S3 patch. All is well again. Given we get 200 for the wipe, install and restore we thank everyone that makes and uses registry cleaners.
I put my computer to sleep the other day and noticed that the fans were still running (S1 state). Normally, all fans power off (S3). I have not changed any settings in the bios or in Windows. Curious, I reverted to a 3-week old Ghost image, and the computer was able to go to S3 sleep. So some piece of software or driver must have changed Windows' sleep behavior - this shouldn't happen.
In searching for a solution, I came across dumppo.exe. By setting the min sleep state to S3, I was able to put the computer to the proper sleep state again. Out of curiousity, I reverted to the old Ghost image again (with working S3 sleep), and dumppo.exe reports that minimum sleep state there is S1. Now, I'm confused. What other setting could trigger or prevent S1 vs S3 sleep in Windows? (remember, no bios setting has changed).