The Photos section of iCloud has been frozen on my Windows 10 PC as well.
It lists 10,000 photos to be uploaded but they never seem to complete even after several days.
iCloud for Windows really needs more real-time display of its progress. it seems to poll for the number of files uploading and then locks in place.
You an check C:\Users\YourUsername\AppData\Roaming\Apple Computer\Media Stream for recent date modified and see if it is doing something. You can also check task Manager and then go to the Performance Tab and Click on Resource Monitor. From there go to network Connections and see if iCloud photos.exe is sending and receiving bits.
As for me I have given up on the Windows Version of iCloud until the Photos Upload becomes clearer as to what is happening. I recommend the Windows iCloud App display more accurate and up to date statuses of Photos being uploaded and also that it wouldn't just sit there doing nothing.
The Web GUi actually works quite well to upload the occasional file from a non-Mac Computer. The Alternatives like DropBox, Box, Sync.com, SugarSync, pCloud, Google Drive all cost more than iCloud and have there own set of issues.
I wish Apple would pull the Windows iCloud version off of the market or else invest it in it a little more to let us know the progress of what is happening and whether is frozen for a certain reason uploading Photos.
iCloud Photos and Drive work great on my Mac and iPhone but not on the Windows Client.