Quoted from system11:Give it a close up visual check. Most of the time you'll see a crack when solder is the issue.
I've had situations where there was nothing visible but reflowing the solder fixed the problem as well. I would recommend getting a temp controlled solder station. They are not real expensive and will be easier in the long run. If you are going to replace say a resistor or transistor that went bad the soldering station is an excellent thing to have.