After looking a bit on the web, I decided to take this problem here, in case somebody has already a solution, or to answer it myself, should I find the Answer.
Setup is like this:
ASUS Maximus V Formula SSD & 3TB WD & 500GB Samsung & DVD & CardReader installed Randomly there are further Drives attached
Two Win7 Systems, one on the SSD, one on the Samsung
The 3TB Drive suddenly turned to a "blank" hdd, which needs formatting - based on how long you wait, it would be shown as RAW or NTFS formatted in the Storagemanager, but you cannot open it via Explorer
However this is only on the Samsung-based-System!
When I boot-up the fresher Win7 of the SSD, it is correctly shown as Primary Partition, Base GPT, and al files accessible - ScanDisk with no errors.
It started, after I connected and disconnected some other drives and booted into the samsung system inbetween. Also I added an installation of Acronis TrueImage - a second one, i might add - although, i thought it would just update the other one.
I tried to use DiskDirector on the SSD-System to counter-check and nearly got a heart-attack, because it startet to make the same trouble - presenting the drive as unformatted - and then it was unaccessible too! but a quick reboot and it was ok again, also with DiskDirector.
Using GPT fdsik I created a backup and inspected the drive - there was no indication of a GPT damage and it found the correct partitions. Could it be just a Windows problem?!
What is going on here?!
After some evaluation time i finally started to trust this drive and now this! Luckily i currently have the option with a secondary system, but what if i wouldn't have?
So for any other one's in trouble - keep calm - don't panic-format anything!