1) Open WMC
TASKS menu > Settings > TV > Guide > Download latest guide listings
If you don't have that option you don't have your tuners set up properly in WMC - you need to set up your tuner
TASKS menu > Settings > TV > Set up your TV Tuner...
2) You can manually update WMC, above
3) What remote are you using?
There are currently no free alternative guides in the US that I know of - I would love a link to a valid webpage when someone says there is one rather than saying "you need to download... from ..."
Zap2It doesn't let you download the guide data anymore, they used to, but no longer. There is schedulesdirect.org which is $25 per year (and that's a not for profit organization trying to get the schedules to people who want them) and then you can use BigScreenTV add for WMC ($20 for 2 year license) that puts the data into WMC, which is designed more for our friends in Europe.
If you are not getting a channel (you mentioned PBS), that's not WMC, that's your antenna.