Basically, reflow soldering (on your end...it's actually a manufacturing term) re-solders all the points on your board. It's difficult to do by hand, and there are ways to do it with real tools - however, you can accomplish a cheap way by stripping your motherboard and sticking it in an oven, very similar to the procedure commonly done to dead GPUs.
http/en.wikipedia.org/wiki/Reflow_soldering
Here's a neato way to make a surface-mount iron, which you can use to heat small points to reflow certain places or smaller boards. It would take a while to do so on a motherboard.
http
/www.engadget.com/2006/03/07/how-to-make-a-surface-mount-soldering-iron/