Sorry, there's no "factory reset" for Google accounts or Google products and services. You'd have to go through each product and clean it out of stuff you no longer want.
If your Gmail is not receiving emails, it could be down to various things. The first thing is to check that the email hasn't gone to another folder by mistake (such as the spam folder). Then check your storage level to see if you've run out of space. Your inbox settings might also be misconfigured.