It sound like hardware (motherboard) problem to me.

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>I am installing win7 on a new hard drive and I have run into an interesting problem. The default install causes windows to sleep when idle more than 20 minutes. Several times this happened to me and when I woke the computer and logged back in the computer froze. I held the start button for 5 seconds to turn it off and when I turned back on the computer would not boot. Event the motherboard splash screen would not show. I finally had to turn the power off to fix the problem. At first I thought I had a bad hard drive and event had Seagate replace the first HD I had. I have now changed the power settings to not go to sleep and I will see if the lockups go away but this is very strange. I was wondering if anyone else has seen this?
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>Thanks.