I'm going to assume you're using the SUNE algorithm to orient your corners. That is...
SUNE: R U R' U R U2 R'
ok jupy what does that alg do?!
_._._ _|W._._| | | . . |W| | | .W. | | |_|W._._|_| |_._.W|
Suppose this is your top layer, where "W" represents your top layer colour.
Then, SUNE will ORIENT the CORNERS of the above state.
So, it rotates every corner clockwise except the one in the Upper Left Front position (you can call it ULF).
If only one of the top corners is correctly oriented, put that corner in the ULF position. Then, within 1 or 2 applications of SUNE, the corners will be oriented.
Otherwise, try to position the cube so that when you apply sune, only one corner on the top face will be oriented after application.
If you can't find your case here, then either:
1) You need to look at the top face from a different angle, or
2) One of the corners on your cube got twisted and needs to be twisted back to make it solveable, or
3) Your bottom face corners got messed up somehow.
Go through the list to find your case and follow the instructions.
SOLVED _._._ _|_._._|_ | |W. .W| | | | .W. | | |_|W._.W|_| |_._._|
CASE 0: Solved! Go to the next step :)
SUNE _._._ _|W._._| | | . . |W| | | .W. | | |_|W._._|_| |_._.W|
CASE 1: Apply SUNE once and you're done.
ANTISUNE _._._ _|_._.W|_ |W| . . . | | | .W. | | |_|W._._|W| |_._._|
CASE 2: Apply SUNE once. Then check CASE 1.
HEADLIGHTS _._._ _|_._._|_ | |W. .W| | | | .W. | | |_|_._._|_| |W._.W|
CASE 3: Apply SUNE once. Then check CASE 2.
PI/MAN _._._ _|W._.W|_ | | . . | | | | .W. | | |W|_._._|W| |_._._|
CASE 4: Apply SUNE once. Then check CASE 1.
L _._._ _|_._._| | |W. . |W| | | .W. | | |_|_._.W|_| |W._._|
CASE 5: Apply SUNE once. Then check CASE 2.
H _._._ _|_._._|_ |W| . . |W| | | .W. | | |W|_._._|W| |_._._|
CASE 6: Apply SUNE once. Then check CASE 1.
Feel free to email me. jupy@envs.net