Dear Friends,
I also have spent hours trying to find the solution to this problem of the disappearing external HDD, that appears in the Disk Manager but not in "My Computer", for example, or that appears in "My Computer" but later disappears. This is the ONLY forum where I believe we have finally found the answer. I congratulate you greatly.
It seems to me that the solution that works most often is described by Crackity on first page of this same thread. He said, "After digging deep into windows disk manager, BIOS, etc., I decided to open up my PC and switch the connections of the disks on the MOBO to see if that would help. Then when I looked into the manual of the MOBO I noticed a remark that the System disk MUST be on SATA 1 or 2 and the Data disk MUST be on SATA 3 or 4. I followed this instruction and everything works just fine again."
My only issue is that I am not a programmer nor an I.T. man; I work with graphic design and music editing, among other things. Consequently I need the help of you technical experts regarding only how to IMPLEMENT the solution given above, on my own Vista laptop. Please kindly help an ignorant guy with a simple step-by-step explanation of how to switch the connections on the MOBO (whatever that is), so that I can assign my two external Seagate HDDs to SATA 3 and 4.
I am guessing that this will involve re-booting the computer somehow in DOS, and making the adjustments there, but I do not know how to do that.
And if you will excuse my additional ignorance, I must say that I do not know whether these drives are SATA or IDE. They are 500 GB Seagate GoFlex Free Agent drives.
(Interestingly, I had bought one in 2010, and returned one year later, to buy two more, and yet the first one has NEVER presented a problem on any of my computers, but the later two have. The latter two were otherwise COMPLETELY IDENTICAL to the first, except for an "updated" software and drivers on the drives when I went to install them: this is where the problem began to occur. In fact I have even tried reformatting the two new ones, and copying over the drivers from the older one, including all "hidden files," but to no avail. Maybe I did something wrong there also.
At any rate, please show me, step by step, how to re-assign these latter two drives to SATA 3 or 4, and I will be grateful.