Another home network problem

I have a desktop PC wired to a [Draytek] router and a new laptop with a wireless connection which works OK.

I can view desktop folders on the laptop without problems, but cannot view laptop folders on the desktop. When I try to access the laptop from the desktop via "Windows Security, Enter Network Password" always fails. The domain is the name of the desktop. I've tried various 'names' in the account field but all I get is "unknown user name or bad password".

I've tried to join the desktop's homegroup from the laptop
but when I type in the password to join the homegroup it tries for about a minute then tells me to run the troubleshooter which unsurprisingly doesn't help.

All I can find is that Teredo is disabled on the desktop. Actually it seems to be completely absent and I can't find out how to install that. I've tried the "netsh interface teredo set state enabled commands" I found in this forum, but that fails with "The parameter is incorrect". I seem to recall disabling Teredo sometime ago when setting up the router, and I assumed it would be a simple matter to re-enable it, but it's nowhere to be found (I've looked in the 'hidden Network properties'). All the IPv6 stuff seems to be enabled.

I had ZoneAlarm on the desktop but have uninstalled it and I've disabled the 'Free Trial' McAfee firewall so both machines are using Windows firewall.

It all seems quite mad

Can anyone help please before I throw the laptop at the desktop?

Many many thanks for a solution....

Solved it
Set Network and Sharing Center / Advanced Sharing Settings as follows
(the quickest way to get to this is to type 'sharing' (no quotes) into the search bar of 'Start', then it's the second item.)
Network Discovery: On
File and Printer Sharing: On
Public Folder Sharing: Off
Media Streaming: ? (don't want to do it)
128 bit encryption
Password Protected Sharing: Off **
Allow Windows to manage Homegroups

** I assume shared stuff is still only visible within the network, and so long as that is password-protected outsiders can't see anything.

This seems to be the only combination of settings that lets me share in both directions.