i had the same problem with my iphone 4s!
it wouldn't charge when i plugged it into the wall OR into my computer, but i tried it with a new chord and it worked fine!
if you've have your chord (the one that plugs into your iphone + an USB slot) for a long time or if you yank on it a lot or are...
something similar happened to my 4S a few days ago: my instagram would freeze for a few seconds then automatically close whenever i opened it.
i solved it by turning my phone off for a few minutes (actually power off) and then turned it back on a few minutes later and then it was fixed :) maybe...