The problem you are encountering is a common defective of not just this model but of many sanyo and vizio sets.
Sanyo hands down make some of the finest economy line sets on the market, they are well supported and for the most part well made, unlike there counter parts of a sim. price.
First thing to try is to cycle the power on all connected devices, ie dvd players, cable boxes, game system anything connected via HDMI. disconnect the power from the wall wait 30 seconds and power back on... this goes for the TV as well. To be honest this only fixes a handful of sets a year but worth a shot.
Otherwise you need to try a hard reset of your sanyo set. To do this is simple here are the steps:
1. remove the power cord for the outlet wait 30 seconds.
2. hold the power button on the set
3. reconnect the power cord to the outlet while still holding the power button
This will clear the eeprom of flash data like old closed captioning data last channel and last volume setting also it will reset the HDMI controller IC and that is what we are trying to do.
This is also not a sure fire fix but worth the effort.
Last thing is the bad new if these simple fixes do not resolve the issue you may either A have a defective HDMI cable or you have the most common defect of all HDMI connection... a failed HDMI controller IC... in that case the solution is to have the set serviced where they have the very expensive tools required to change the actual smd integrated circuit (IC) or to out and out just replace the main board.
If you choice to do the repair yourself the board replacement is simple enough you will pay 3x what a service center pays for the part but you can save some of the cost by having no labor cost which are anywhere from 65-150 depending on the shop.
Part # XXXXX
(it is crazy how simple sanyo part numbers are 4 digits sometimes 5)
You can order the part from sanyo but they dont like selling to customers the part is right around $150 from them for most main boards.
or you can search ebay for a board number 1LG4B10Y04600 which i found a few but not many. The board is simple to replace plug and play for the most part a few connectors and some screws.
Hope this helps,
If you have any questions please just ask.
(sorry took me a while to type out 5 minutes to say 10 to type)