Hi Jonas,

If you Remote desktop doesn't work when connected to a Windows 7 or 8 PC and you see only a black screen, then the connected computers involved might be having an issue with the screen resolution.
You can resolve this by following the below steps:

1. Click on the black Remote Desktop windows (to select it) and press CTRL+ALT+END to bring up the Windows Security screen and select LOG OFF, then log back in.
2. Start a new Remote Desktop client on your desktop but before you click CONNECT, click the SHOW OPTIONS link, click the display tab and set the display configuration to a low resolution such as 640×480.

If the above fix didn't worked out, you can use this fix as well.

1. Logon to the Remote Desktop Services Session Host computer as an administrator. Go to Start–Run gpedit.msc
2. In the left pane, under Computer Configuration, navigate to following: Administrative Templates\Windows Components\Remote Desktop Services\Remote Desktop Session Host\Remote Session Environment
3. In the right pane, double-click on Set compression algorithm for RDP data
4. Select Enabled, and choose Balances memory and network bandwidth.
5. Click OK to save the changes.

Also ensure that you are using the same version of the RDP client on the computers you are connected. For eg: use 6.0.0.1 on both the computers.

I hope this helps in solving the black screen issue in your screen sharing.

Regards,
Lokesh