Velcro is formed of two parts - one side is loops, the other hooks. If velcro wont stick (assuming it's not gummed up with fluff) it either means the loops have become torn or the hooks are broken/straightened or both. If so then there is a small chance that the material that the velcro is made of has an "elastic memory". If so then this may be activated by heat. Try warming the velcro with a hair dryer - enough to make it hot but not quite enough to melt it! Once cooled, this may return a degree of stickiness but certainly nothing like new.