computer slows down when connecting Ipod or other external USB mass storage device

A customer had a problem with his Ipod, when connecting it the computer would slowdown, the hard drive would start making strange noises and itunes would not recognise the device.
So the first step was to remove and reinstall itunes and the Ipod but with no success as the problem persisted.
I then decided to change the hard drive for a new one since it was making strange noises I thought this was the problem but again the problem persisted I then decided to format and reinstall windows onto the new drive ,keeping his old system on the old drive in case the format didn´t work I had a backup.
I did the format and reinstalled windows the Ipod and itunes, it started to work fine, managed to detect the device and copy music from the computer to the Ipod when all of the sudden the computer went slow ,hard drive made clunky bad sounds and the copy process did not complete with an error.
Frustrated i decided to change hardware parts I changed the easiest one the power supply and behold all worked fine.
no more slowness ,clunky noises and managed to copy over 200 songs to the Ipod with no errors even put back the old drive with his system and it also worked.

Its just a reminder that there is always a way to fix these problems it just takes time.