I usually use box cake mixes and I bake them the day before but when I go to cut them its still really crumbly, especially when I crumb coat. and then when I frosted it was still crumby the crumb coat didnt work so well! Any Ideas?

Welcome to CC, Ashleymamaof4.

Decoding CC acronyms:

http://forum.cakecentral.com/cake-decorating-ftopict-2926-.html

Straight cake mix cakes shouldn't be that crumbly...

Are you crumbcoating w/thinned frosting. If not, you're actually pulling off the outermost layer of the cake each time you lift your spatula from the cake surface. (NO cake layer, box, doctored or scratch could hold up to this stress.)

Cake troubleshooting charts:

http://tinyurl.com/2p5bdu

http://tinyurl.com/32goqe

http://tinyurl.com/6c745g

Everything you ever wanted to know about making your 1st tiered/stacked cake:
(Has WASC cake recipe w/variations, popular CC b/c recipes and so much more baking & decorating help.)

http://forum.cakecentral.com/cake-decorating-ftopict-605188-.html

Secrets to Cake Carving:

http://forum.cakecentral.com/cake-decorating-ftopict-605906-.html

HTH