Hi msguppy,
Welcome to the HP forum!
Thank you for your post, I will do my best to help.
I understand that it was working, but now you have no sound. Here is a link to No Sound from Speakers (Windows 8). If this has not resolved your issue I would sugget calling HP Tech Support as you are in warranty if it is only about 1 month old.
Please call our technical support at 800-474-6836. If you live outside the US/Canada Region please click the link below to get the support number for your region. http://www.hp.com/cgi-bin/hpsupport/index.pl