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Delayed boot

When I power  on a PC the very first screen of Intel splash logo  stays there on more than 3 minutes then it boots the windows. normally this screen only take few seconds. there is no beep sound hear while booting.
I suspect some  hardware problem the PC .so while performing post test the problematic area  cause the lengthy boot.
so i did the  following procedure to  pin point the problem
  1. switch off the PC 
  2. removed hard disk ,CD ROM  and floppy connectors
  3. remved all internal USB  and front audio connection
  4. switch on the Mother board , 
  5. still problem is there
  6. Replace BIOS Battery found it is 2.7 v instead of 3 volt but it is not the culprit.
  7. Clean RAM and  and check CPU FAN ,even apply enough heat sink compound to the processor.
  8. Remove dust in the mother board with compressed air
  9. Inspect any visible burnt or damaged component in motherboard .
  10. check capacitor in the motherboard. 
  11. power on the PC still the problem is there.wait more than 3 minutes to load windows completely. 
  12. Normally during the boot some numbers and letters running in bottom right edge of splash screen which give hints about post codes.But in this case no such numbers appear.
  13. after windows loads I check the device manager and  found 4 unknown devices in the USB area.and not any USB device detected in any USB port.
  14. I suspect USB controller causing the boot delay
  15. restart computer pressing f2 and enter the bios disable USB in bios,save exit
  16. Now the computer restart and boot without any delay
  17. add a 5 port pci USB add on card in the PCI slot and tell the  customer to use that USB port,here after,
  18. This by pass surgery  save a motherboard  now the system is ok

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