Quote:
what can I do in this case? Re-heat the solder joints for the header?


Simply go through all of the bullet points in the appropriate FAQ entry, read them carefully, and do what it says.

Quote:
I think I can exclude the cable as a problem at this point, as I get the same problems no matter on which connector I connect the hard drive; is this correct?

No, you've merely verified that the problem happens on both connectors, meaning that there's a possibility that both connectors could be the problem, or that it's not the connectors at all and is any one of the myriad other bullet points in the FAQ, or that your problem is completely unrelated to the hard disk at all.
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Tony Fabris