Assuming the form on your site was working, it's possible it's suddenly stopped, but more likely the emails that it generates and sends have started to get tagged as spam and so are winding up in your spam box.

So, if messages from the form on your site are not arriving in your inbox, first check the spam box, better still, do a global search of your email service for the subject line of a recently completed form.

If the email from the form has ended up in spam, mark it as "not spam" and carry on. If not, get in touch.