@sonarctica,
What is the make and model number of your Motherboard?
Based on your last post, Legacy Drivers in Device Manager+Folder Permissions need checking. There could be one or more legacy drivers conflicting with (slowing down) accessing the WD passport. And "not accessible" may be due to folder permissions or the lack of.
1. Check Device Manager for Legacy Drivers. Meaning, see whether or not in Device Manager, if the "USB 3.0 Host Controller" or "USB 3.0 Root Hub" are using Microsoft Drivers. They should be using the Motherboard's Chipset/USB chip's drivers.
(As many as possible of all your Legacy Drivers should be updated; but focus on just USB 3.0 for now. See, Microsoft OSs these days always seem to install Legacy drivers for everything; but cool np; think of it as being just so that you can see the Names of all devices. Without Legacy Drivers they would not say anything but "Unknown" in a category called "Unknown". But, Nobody seems to ever update them. Let alone check for Updated updated Drivers. lol Ppl just keep building new PCs when all they really needed was to update Legacy drivers.lol Over time, Legacy Drivers can gradually make things worse because updated Drivers have fixes built in whereby Legacy drivers don't. I went months before realizing it with each MS OS after WinXP. But now, ALL of my devices that can be updated are updated. Just around 33% of all of them must remain Legacy Microsoft Drivers; all the others should be updated to Chip-set Drivers: if, you want optimal performance.)
2. As far as Folder Permissions (and this happened upgrading from Vista to Win7);
Right click Drive Letter (K), select Properties, and Go to Security Tab;
and you may see in the box under "Group or user names" that your user, is not listed; and/ or that one or more enigmatic user names ARE listed. If so, add your user, plus give it all permissions. You may have to take Ownership 1st in the advanced section. And that, is the really tricky part.
Also because you upgraded from Win7 to Win8.1, check MSConfig's Start-ups.
GL 🙂