I'm having trouble with one of my Windows 8.1 PCs. It has 4 internal hard drives and only two of them are showing up in Windows Explorer. I see all of them in Disk Management but it gives me an error if I try to give them a drive letter:
It also doesn't mount external drives when I plug them in. They were all working before the upgrade in Windows 7. This PC has an Asus P8Z77-V DELUXE motherboard if that helps any. I can confirm all the drives themselves are good.