Debug website issues

I need some help with my ecom website. It didnt have my attention for a few months and now there are a few issues. It seems to be broken. First of all I've just tried registering to my own website with different email and I didnt receive email confirmation email. I also see alot of people trying to pay (in wp dashboard) but payments are not being collected. Are you able to debug registration and purchase errors? Basically try to imagine as if you are a customer buying a file from my website and debug and fix the issues?

I use wordpress site with jobster theme.