Can I get a very detailed (services involved etc) explanation of the Windows XP Driver Signing process? Every now and again I get a PC that has no USB functionality. Sigverif.exe claims that over 2000 drivers are not signed. A healthy computer built from the same image has far less drivers listed as unsigned. The list includes things like USBSTOR.SYS, which is definitely signed. Most of the Microsoft drivers which were seen previously as signed drivers are now seen as unsigned. I even tried replacing drivers with the original and it's still detected as unsigned.
The keyboard and mouse are non-functional when this happens. The only fix is to re-install Service Pack 3. The issue comes back approximately 3 months later on some of the computers. Thanks for your help.