Assuming your kite is not damaged there are very few things that can go wrong with a Power Kite.  The common symptoms and solutions are listed below:

Kite will not lift off the ground.

1. Is there enough wind?  Obvoius really, run backwards faster does the kite take off then?  Wait for a windier day.
2. Are the brake lines too tight?  Point the brake end of the handles as far towards the kite as you can, does the kite take off then?  Also try shorten the power lines, by tieing a knot further up the power leader lines at the handles and larksheading the power lines behind that.   If that's the problem try equalising your kite lines.
3. Is the bridle tangled? - Carefully inspect it to ensure no bits of the bridle are caught round each other.  Pay attention to where the lines are attached

Kite lifts of ground then always turns to the ...

1. Are you holding the handles equally? - Make sure your hands are together on launch
2. Are the lines equal length? - Try equalising your kite lines.
3. Is the kite set up properly?  Lines attached correctly?  Look at out guide on setting up your power kite.
4. Is the bridle tangled ?- Land, inspect and untangle.

Kite takes off, but is difficult to control and crashes.

1. Maybe pilot error - use smaller movements, hold your hands together and only move them tiny amounts

One tip of the kite always looks crumpled.

1. You have a bridle tangle.  Land the kite, inspect the bridle carefully and untangle.  Sometimes you can shake out the tangle in the air by pulling on the lines.

Kite will not fly above me ... only gets to 45 degrees.

1. Are the brake lines too tight?  Point the brake end of the handles as far towards the kite as you can, does the kite take off then?  Also try shorten the power lines, by tieing a knot further up the power leader lines at the handles and larksheading the power lines behind that.   If that's the problem try equalising your kite lines.
2. Is there enough wind?  Run backwards faster does the kite go higher then?  Wait for a windier day.
3. Are you using the right lines?  Are they to heavy or long, causing too much drag
4. If your kite has variable angle of attach AoA (a AAA bridle), then reduce the angle of attack

Kite overflys above me, and falls into a crumpled heap.

1. Some high performing kites are designed this way?  Redirect the kite, or use the brakes to keep the kite from overflying
2. Fit power rings  Some kites benefit from a line cross connecting between the power and brake line.  Google 'firebee power rings' for more info.
3. If your kite has variable angle of attach AoA (a AAA bridle), then increase the angle of attack