for the last several weeks, ever since I started using Inventor for my graphics class, I've been able to easily make 2D sketches and extrude them just by drawing lines. I start one at another's endpoint, make a rectangle or triangle or whatever, click "finish sketch" and then it lets me extrude. Suddenly today, it won't recognize closed areas unless I add "coincident" constraints. Also, half the time after I add the constraints, the lines jump to a spot that's clearly not attached and not making the triangle that SHOULD be easy to draw.... I just don't understand why simple sketching has turned into a nightmare. Is there some setting I might have changed?
This is not an expert response, but I do use Inventor every day.
It sounds to me like you perhaps have changed the origin point for your sketches. The best way to walk through this is to see what you are doing.
Please send me an email and I will assist you.
A suggestion for your sketch is to make sure it is fully constrained. You can check the degrees of freedom by using a mouse right click and select the command [Show All Degrees of Freedom] This will help prevent geometry changes when a sketch is inadvertently moved. Also you will see the notation in the bottom right of the status bar stating the number of dimensions required to fully constrain the sketch. Hope this helps.