05-10-2017 02:16 PM
Welcome to HP Forums, this is a great place to get support, find answers and tips.
Thank you for posting your query, I'll be more than glad to help you.
I understand that you are unable to print from your HP DeskJet 3720 All-in-One Printer and the letter E keeps flashing.
This issue could occur if the printer is in error state.
Let's go through a few steps to troubleshoot this issue.
And here's the step by step guide for you in the link: Blinking Lights
Let me know how this works.
You have a good day ahead.