I have played this game since June 14. I have probably restarted the whole game a number of times (20 times or more). On steam it says I have played 804 hours. The problem I have now is that quests don't start. Like at Saarthal, I talk to Tolfdir and return to Winterhold to talk to the Arch-Mage, it works fine until it gets to the point of going to get the books to finish the orb quest, it just quits at the arch mages room. Then the thieves guild, I go to the three deadbeats and collect the money then Brynoff just says his part and that is the end of that. Can't even join the thieves guild, so that quest won't work anymore. Then to Solitude, the guy doesn't show up to complain about the wolves cave so I can do that quest. I don't know how many more quests won't work but It seems that maybe I should reinstall the game? Any thoughts?

Are you using any mods?

...and have you installed the unofficial patch(es) as well ???

the unofficial patches won't make quest start if something is broken in his game.

@ OP: is your game up to date? Reinstalling is a good idea, or maybe you don't remember how to play and you overlook things?