Photo Stream isn't actually physically stored on a device, it's in iCloud to be shared between devices.
Try installing this:
Edit: Are you trying to just place copies of the photos on your Windows PC or are you also trying to completely remove the originals from the phone? If you're just trying to copy them, the above should work. Let me know!
This should help:
It requires the iCloud control panel I linked you to previously. Remember, photo stream pictures are not on the actual device. Pretend they're photos on a website, and every device that can view them is just pulling them from that website. Inside the iCloud control panel you can delete them from Photo Stream, effectively removing them from any device that can access the stream. Let me know if you need any more help with removing them.
As for accessing them on Windows, I am still assuming you installed that control panel. You did, right? When you open it, log in with your Apple ID. Make sure "Photo Stream" is checked. I don't have a Windows computer to verify on, but I am fairly sure that once you activate it you can click "Options" to determine where those pictures go on your computer, so just pick a folder (such as 'My Pictures') where you want them saved. Do that BEFORE erasing the photo stream, though, because if you delete them then there will obviously be no pictures to download to your computer.
You clicked "Options" on the "Photo Stream" one, right? It looks something like;
[Checkbox] Photo Stream [Options Button]
Did it give you the ability to select where you wanted the photos to be saved? If you've already selected where you want the photos, give it time to download them.
This is from Apple's knowledge base:
"On a PC, your photos download to the Photo Stream download folder. By default, this folder is located at C:\Users\Apple\Pictures\Photo Stream\My Photo Stream. You can change this location by visiting Photo Stream Options in the iCloud Control Panel for Windows."
Check that folder if you did not select another location for the photos. If you still do not have any photos, there's one more thing we can do to fix it:
1. Close the entire iCloud control panel.
2. Open your task manager (ctrl+alt+del, it will either bring it up or bring up a screen where you can click task manager)
3. go to the "processes" tab, sort by name, and close any processes from apple or icloud (right click the process and hit end process)
4. Once all of the processes are closed, reopen the iCloud control panel software and see if the download begins.