Kartoom! Can someone please point me in the right direction, preferably not Oblivion. I have the first two pieces of Gualdour's amulet, but at the ruins for the third piece, I need a key to get in. I have the key from the battlemage in the second ruins. So, where to next? I find no clues where to head.

I assume you mean Saarthal?
Try speaking to the bouncer on the steps of the big College in the nearest large settlement, and then go from there.

I'm guessing the ruin is Saarthal? You have to join the college of Winterhold for that one. One of the first quests should take you into the ruin if I remember correctly.

Where are you? Folgunthur? Saarthal? or Geirmund's Hall? If you're trying to enter Saarthal, go the College of Winterhold and enroll. They'll let you in.

I assume its Saarthal the op is refering to. Only one with a key you need the mage to get in.