Hello TES forum.
I was playing skyrim on the PC recently when a strange bug happened:
I was playing through The Thieves Guild questline (major spoilers)
But when i came out of the Bronze water something cave after killing Mercer Frey and i was told to take the pilgrims path.
I was not able to talk the sentinel/Gallus. I didn't give me the option. I thought it was weird and tried fast travelling to the Whiterun stalls where i could not speak to anyone either.
(pic here http://cloud.steampowered.com/ugc/541810681088144888/E0B1B4529DC4B59433B68EB3D0EE6DC9FFF76FC3/ the E talk thing is not there)
I tried reloading old saves but it was the same (strangely it has only happened to this character since i tested it on my two others).
I even took a save from before i joined the thieves guild. Still nothing.
I have tried restarting my computer too. Please help me.

You should check out your mods pal.. some of them probably got an update with a few issues.