First do a visual check. Looked for cracked solder or damaged components.

The image on this page shows a wire who's solder has completely detached from the board.

To fixed cracked or detached solder, use the soldering iron to heat the solder already there until it flows and becomes completely attached to the board.

To replace damaged components use the iron to remove and replace them.

If you haven't soldered before check out this guide.