Keef, been there, done that, got the tee...
As well as Richard's suggestions, I've had these problems so often now that I always check that one of the machines - usually the laptop - hasn't got a "Bridge" in the Network Connections. If it has delete it. Your laptop and desktop may be looking for each other on different LANs.
Right click on the Network Connections that you think should work and click "Repair".
Good Luck.