I am very confused. I have just had to format and re-install Win 7 due to a massive system upgrade. I have 2 Hard Drives installed in my PC and 1 of them has now vanished. I have checked the BIOS and it appears there and it is also in the System setting, heck I can even defrag the dam thing except it does not appear in My Computer at all, in fact it appears everywhere else except My Computer so therefore I can't access it.
I followed your advice and it asked me to allocate a drive letter to the drive so I picked E. I can only think that as Win 7 allocated D to the DVD Drive (the invisible drive was previously D) it would not recognise 2 x D drives so it just ignored my other hard driv..........does that make sense? Anyway all fixed now