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#11
How soon after you reinstalled Windows did these problems occur? Did you reinstall using a manufacturer's hidden recovery partition or from an actual installation DVD? If from a DVD it's possible the installation got corrupted in some way. Did you also apply all Windows Updates (including SP1) after you reinstalled? Sometimes updates can cause system glitches. Since the system file checker scan didn't find anything you might be able to find something in the Event Viewer logs.
What information appears in event logs (Event Viewer)?
If nothing jumps out as a significant error you might consider a repair install using the installation DVD, or if you used the hidden recovery partition, try that again.
Repair Install