I have a Windows 7 64bit with 500GB on the OS, then I added 2TB hard drive (Hitachi) to the system (for movies and stuff) and when it was full I added another 2TB hard drive (samgsung) for more movies and more stuff, recently I have been having this weird error.
Suddenly the hard drive dosen´t show on Windows/My Computer nor in Disk Management and I can´t access it, but if I reboot Windows it will appear once again, but when I want to transfer some information it starts at 100Mb/s but then falls to 1Mb/s, and after a while it won´t show up again.... I did a HD Tune test when it was available and the results where perfect, but then after 5 minutes the HDD dissapeared once again. I updated the BIOS and nothing happened, what can it be????.. can you help me?