All of a sudden, none of my users can browse our network. All Services are running, and only a few PCs show up....Any ideas?

Go to your server manager on your PDC....select computer...synchronize entire domain.

Did it....didn't help.

Check event viewer to see if there are any errors about licensing. Try disabling the license service or adding more.

The Event Viewer Error says..."The browser service has failed to retrieve the backup list too many times on transport\Device\NetBT_E100B1. The backup browser is stopping. Any suggestions??

Your PDC is your master browser/domain master browser by default. Your BDC is most likely your backup browser. For some reason the backup browser service is not functioning properly, your network should have automatically performed an election to choose another browser. You can disable the browser capabilities of the problem computer (see event viewer) and another computer will be assigned the role. Search the registry for MaintainBrowserList (no = non-browser, yes = will be master/backup, or auto = based on election). Also there is a IsDomainMaster key, if this is set to 'True' then this computer will always be the master if the PDC is unavailable. Hope this helps!

Thanks for the help guys. The problem turned out to be totally non-Microsoft related....We had 2 Linux Samba Servers on our network, and one of them had the "Preferred Master" variable in the smb.conf file set to "ON", so everyone was looking to these Linux boxes, that don't use NetBios. Learn something new everyday.