Okay got it working, thanks for the help guys. The problem was that all my media is on an external hard drive. In case anyone else has this problem and stumbles upon this thread, here's what I did:
1. Right clicked the external hdd and went to sharing tab. At the bottom it said that I had password protection on, so I followed the instructions there to disable it.
2. The 'Share' button in the sharing tab was greyed out so I had to go into advanced sharing and check 'Share this folder'.
3. I then went into the security tab of the properties pane and gave my user account all permissions. My user account is the only account and therefore has admin rights, so I don't know why I had to do this.
4. I then created a new username called 'everyone', and gave it all permissions.
5. Clicked okay and close, and I could then access it via ES on my prime.
The reason I didn't mention the hdd in the OP is because at that point I couldn't access the laptop at all. Once I did the above everything worked. I think having password protection on was preventing me from getting into my laptop at all, as I don't have any passwords in windows.
Thanks for the help! I now have access to all my media on my prime. Good times.
EDIT. Turns out the username 'everyone' doesn't need all permissions. I didn't like the idea of 'everyone' having full control over my hdd so I changed the permissions to just allow reading and writing, no modifying etc. Still works.