A friend of mine gave me this puzzle to work because he couldn't even get started. With complete confidence in my solving abilities, I told him no problem. But there is a problem, I cannot even find a single candidate even after two hours of trying. My humility has returned and I need help to even know where to start. This is embarrassing and I hope somebody can at least point out what I can do to begin this puzzle. Is this a tough puzzle or have I missed something that is rather obvious? Thanks for your help.
*-----------*
|1..|.5.|..9|
|...|1..|.3.|
|..8|...|2..|
|---+---+---|
|.5.|..4|...|
|4..|.6.|..8|
|...|3..|.1.|
|---+---+---|
|..2|...|5..|
|.3.|..5|...|
|7..|.9.|..2|
*-----------*
*-----------*
|1..|.5.|..9|
|5..|1..|.3.|
|..8|...|251|
|---+---+---|
|.5.|..4|...|
|4..|56.|..8|
|...|3..|415|
|---+---+---|
|..2|...|5..|
|.3.|..5|...|
|7.5|.9.|..2|
*-----------*
*--------------------------------------------------------------------*
| 1 2467 3467 | 24678 5 23678 | 678 4678 9 |
| 5 24679 4679 | 1 2478 26789 | 678 3 467 |
| 369 4679 8 | 4679 347 679 | 2 5 1 |
|----------------------+----------------------+----------------------|
| 2389 5 179 | 2789 1278 4 | 679 2679 367 |
| 4 179 1379 | 5 6 1279 | 379 279 8 |
| 2689 6789 679 | 3 278 2789 | 4 1 5 |
|----------------------+----------------------+----------------------|
| 689 14689 2 | 4678 13478 1678 | 5 46789 3467 |
| 689 3 1469 | 24678 12478 5 | 16789 46789 467 |
| 7 1468 5 | 468 9 1368 | 1368 468 2 |
*--------------------------------------------------------------------*