So I downloaded winterboard and some themes for it but I can't figure out how to "activate" any of the themes... I click on them and the check mark appears and then it resprings but the theme didn't take effect... What is going on?
Try turning on Summerboard mode. That will most likely fix it.
It is on :/
If you go into settings and 'reset all data' (don't worry, you won't loose any data doing so) and your iPhone resets and stalls in safe mode then the theme(s) you have loaded in winterboard are not compatible.
Remove the theme through Cydia and turn your iPhone off and then back on.