I'm have this problem where my drives including DVD aren't showing in My Computer, but I can see them under device manager and disk management.
Changing the letter of the affected drive will bring them back, but it will disappear again, if I click on refresh or close/open My Computer.
Restarting helps but it's just a temporary fix as sooner or later the drives will disappear.
One weird part is I have a 2TB split two even partitions. The first partition doesn't have this problem, but the second partition does.
e.g. 2TB got the drive letters G and H. G drive runs great, does not have this problem. H drive has this problem.
Intel Xeon quad core
Asus Ramapge Formula (s775)
Intel 120GB SSD (Boot)+WD 500 Black (Data) <--These drives don't have that problem
2TB WD Green <-- 2nd partition has the problem
500GB WD Blue <-- has that problem
DVD writer <-- has that problem
Windows 8 Pro 64bit with Media Center