Thanks for the reply.
If the picture came right back on, it could be due to the cable box, HDMI
cable, or the TV itself.
Was the screen still lit when the set was showing no picture and no sound?
If not, were you able to pull up MENU or change Input- or anything?
If not, then you have an intermittent fault in the TV- which isn't uncommon when parts start to fail.
If there was no response from power (no change in screen, no click no change in power light, etc.), then you're usually looking at needing the Mainboard replaced eventually. This is an average of $250 parts and labor.
If the set clicked on however, and nothing displayed on the screen- and no sound, then this is more in line with a power supply board fault occurring- and is around the same cost.
If you run into the issue again, or more frequently and it doesn't turn on- then you can use the link below to locate a tech in your area if you'd like:
Alternatively if you're a DIY type and have a multi-meter I can also help you perform your own repairs.
If you need further assistance let me know. Please do not forget to click a POSITIVE RATING before you go- as it's how I am credited for my work. You can follow up at any time, at no additional cost.