To check if I had my PCI BUS ID's correct I did $ lspci | grep vga which had showed me the Bus ID's yesterday but today gave me nothing at all.
This thread is pretty old but I figured I'd add on to this thread for posterity as I'm troubleshooting the same issue. I have not figured out what's wrong with my system but your command has a minor typo in it that caused it to give no results. VGA should be capitalised as grep is case sensitive.