Have you tried changing the needle? Often that's what causes skipped stitches. Make sure it's inserted all the way up in the shaft and is facing the right direction. You may need to use a guide to get your seam allowance, like a piece of tape or stack of post it notes.
Here's some instructions on how to post pictures. If we could see the problem, we might be able to help more...
First do this:
http://www.quiltingboard.com/qb-help...g-t166655.html
Then do this:
http://www.quiltingboard.com/qb-help...s-t168819.html