Windows 10: Cannot browse upstairs PC from Downstairs

I can see both Windows 10 PC's listed in Windows Explorer (under the Network tree on the left hand panel).
I can browse both computers from the upstairs computer.
I cannot browse the (Ethernet wired) upstairs computer from my downstairs (wireless) computer.
The upstairs computer first asked for my downstairs Windows login, which I gave, and I was able to browse my downstairs PC from upstairs.

There are two accounts on the upstairs computer and I can access both after entering their individual credentials. When I try to browse the upstairs computer from downstairs it prompts for the upstairs computer's username and password (for some reason the name of my downstairs PC is listed as the domain in the popup window). The username/password combo is rejected. I've tried every credential used on the upstairs PC but none are accepted.

I opened the Credential Manager and there are no Windows credentials listed on either PC. I added a credential to the upstairs PC but I still wasn't able to browse it from downstairs.

If I can't browse the upstairs PC from downstairs then I don't want the upstairs PC to be able to browse my downstairs PC. However, I can't find a way to retract whatever permission I gave the upstairs PC. Upstairs users have free reign to browse my User and Public folders.

I'd appreciate any help to allow me to access the upstairs PC or to force the upstairs PC to enter my credentials for access as before. Thanks.

:)

 

View video on TV

Here is my problem :

My TV (Sony Bravia) is upstairs in the livingroom.

My PCs are downstairs, one running Windows8.1, one running Windows10.

All connected with cable-LAN.

Until last week, both PCs were running Windows8.1, and I could view

videos from both PCs on the TV.

But after I installed Windows10 on one PC (PC10), I cannot access videos on

that PC from the TV.

I know I can use "Cast to Device" on PC10, but that is not practical,

having to start the video on the PC10 downstairs and then rush upstairs

to watch the video on the TV.

 

more problems than i can count with windows 10

Not kidding about the other stuff. PS4 1TB downstairs, PS4 500GB upstairs, Apple TV downstairs, old Apple TV upstairs. Samsung TV downstairs, Samsung TV no wifi upstairs, ipad air 1 & 2, 2 older ipads not figured out what to do with yet, two galaxy note
5's, another Samsung phone cant remember what model. 2 old HP laptops, 1 MacBook pro, 1 Kindle. May sound like a lot but when you think about it, probably similar to a lot of households when you've got enough people. None with any issues connecting to, or
downloading stuff from wifi.

 

I was able to access the upstairs PC by entering its username syntax as follows:
username = name_of_pc\account_username
then entered password of that username account)