In reply to bendep:
Enjoying something is the biggest motivator. Once you get back into it, you'll remember why you used to put the effort in, and you'll soon find the motivation pouring in.
Also, don't try push grades you used to climb, you'll only fail and be put off, smash out some easy grades, and work up, you'll pick it up quicker than the first time round, be less likely to injure yourself, and will get a motivating ego boost as you top out time after time.
Good luck.