As an aside, make sure your power supply can handle all the drives you have in your system. I don't think that's your issue but it's an important component to look at while troubleshooting, too.
MS-MVP - Elephant Boy Computers - Don't Panic!
Well, the external discs are USB connected. But Long Test failed on the intern disc.
I think that it may be right that I have too many devices in my system. So before I’ll do something more I decided to shift my data and thru out 2 of the oldest discs. After that I will proceed with the tests and let you know the result.