I doubt very much if there is an obstruction, trees 40m away at the same height as the dish would definitely not cause a problem. But I agree, a photo would help.
Also Technomate's advice about the declination setting for the dish is incorrect as far as I know. The elevation settings on the other side of the motor are just 90-latitude.
If there are no obstruction issues, I'm wondering if the problem is just inexperience with lining a dish up. In which case I would reccomend having a practice at trying to find a few satellites on the arc manually at ground level.
