Many users of Line 6 interfaces are reporting that their devices have stopped working since they upgraded to Windows 10. Furthermore, there have been reports of PodFarm crashing on opening, and even Line 6 Monkey refusing to connect with the Line 6 servers, meaning the only way to connect is via the Line 6 website.
Even when you eventually manage to open Monkey and perform all the available updates (which state they are Windows 10 compatible), the problem still exists.
Line 6 have acknowledged the problem, and say they are working to update the drivers as soon as possible.
In the meantime, there is a workaround which got me up and running again.
If you still can't open PodFarm to access the ToneDirect settings, open SONAR and try and get in via Audio>Driver Settings.
If you're running ASIO drivers, change to WDM/KS and let the Wave Profiler run. Close SONAR, and now you should be able to open PodFarm.
If you still have no sound, open Device Manager and navigate to the 'Properties' tab of your Line 6 device. Change the settings to 16bit/48000 and you should be good to go.
It's not ideal, but it's a workaround that gets your sound working again until Line 6 sort this out.