Can't get connection to work ("unknown user name or bad password")

So I'm trying to establish a simple connection bewteen a friend and me via hamachi. We both use windows 7.

We managed to create a small network. When I try to access his PC (right click -> browse), hamachi asks me to type in my username and password. I think these are the my windows accounts; so when I do type them in, I get the error message "Logon failure: unknown user name or bad password"

Here is what I've already tried

- put the domain name before the username like this {DOMAINNAME}\{USERNAME} (or with '/')

- remove the password from my username

- create a new windows account with admin rights and log in through that

- Turn off password protected sharing in the control panel

- Try to google it (putting in the error message and various other things)

It used to work before I reinstalled my windows, I remember having had the same problem when we first tried it, but back then the solution was to include the domain name, which doesn't work now.