With Dawnguard loaded there is a marker on the map SE of Riften, but not on the compass. Cannot find this cave I guess I'm suppose to. The marker lies just about at the Standour Followers' Tower. All the guards in Riften are now Imperial guards, maybe because I started the Civil War Quest, either way they aren't useful and don't know anything. Read there was a cave North of Riften, that was a bust too. Any help lacating someone or something to get this thing going would be greatly appreciated.

Are you looking for the entrance to Fort Dawnguard? That's Dayspring Canyon. Follow the road to Morrowind; the cave is on your left.

Yeah, but do you know how far ? I've been looking for it headin north from the stables, stayin on the road and can't seem to find it. I'm sure it's there, just frustrating. Befor I realized it, I was almost at the C

Sorry, got cut off. Anyways, just want to know if I'm headin in the right direction. Really would like to start this thing, but I'm wonderin if I got a glitch cause the marker as I said isn't where everyone else is finding it.

The marker on the map, if the issue is common for all of us, points mistakenly outside the border with Morrowind. However, the cave is a bit before the downhill that leads to the border, on the right side.

If it's just not there, try reinstalling the DLC.

This may help some
http://www.youtube.com/watch?v=W9V_TV9Y_Bw&feature=relmfu

This may be better help
http://www.rarityguide.com/articles/articles/2710/1/Skyrim-Dawnguard-Walkthrough-Part-1-Dawnguard/Page1.html

You need to keep looking in the area of Standour's Beacon, the entrance is not far from there.

If you haven't found it already:

1. Follow the road that leads to the gate of Morrowind.

2. Walk past the bridge.

3. It'll be a little further down from the bridge, look for a down tree log on your left, along with some lights illuminating the cave.