I am having the same problem and emailed Sony this morning. Their reply is below too.
If anyone has tried these solutions, can you please reply and confirm what did/didn't work.
Model : XBR55HX929
Question : I have a XBR55HX929. I turned on the TV yesterday and there is No signal. I do not have cable and for some reason the TV Input was on Cable. I changed to Antenna and it still was not receiving a signal. I tried to run auto-program again and it did not located any channels. I witched to Cable and ran auto-program. It located 3000 channels but since I do not have a cable subscription it was just displaying the Comcast channel. I switched back to Antenna.
I checked the coax cable and everything is connected just fine. I re-ran the Initial Setup and it did not find any channels. I tried to run the auto-program again and this time the screen went black after a while and the TV rebooted. When it came back on the Menu button would not work. I tried powering off and on and it did not change. Then the red light started flashing and I counted 8 flashes.
I unplugged the TV and plugged it back in. Today the red light is not flashing, the menu button works fine, but it is still not getting a signal. I have not been able to duplicate the flashing red light.
Thank you for contacting Sony Support.
I understand that the TV is turning itself OFF and ON and the Red standby light is blinking 8 times.
This is a known issue. There was a Network Outage which has been resolved.
We apologize for any inconvenience caused.
Based on the issue you are experiencing with your TV, I would recommend you to follow the troubleshooting steps provided in the links below and check the operation.
If the issue still persists, please follow the troubleshooting steps below and check the operation:
1. Unplug the TV power cord from the electrical outlet.
2. Allow the TV to remain without power for one minute.
3. Plug the power cord back into the electrical outlet.
4. The TV should turn on. If the TV does not turn on automatically, turn on the TV and return to step 1.
5. Perform a factory reset.
A. After a picture or display information appears, wait two seconds and then press and hold the up arrow button on the remote control.
IMPORTANT: Make sure the remote control is pointed towards the front and center of the TV.
B. While holding the up arrow button, press and release the Power on button on the side of the TV. Reset will appear momentarily on the lower left hand corner of the TV.
NOTE: If the reset procedure does not start immediately after the picture or display information appears, the reset will not work properly. In this case, start this procedure again.
C. Release the up arrow button on the remote control and wait for the TV to reset.
If the Reset message does not appear and the TV turns off and on, begin again from step 5.
If the standby light begins blinking eight times, return to step 1.
6. After the Reset message appears, allow the TV to reset. Do not press any buttons on the remote control or on the TV and do not make any other adjustments for 1 minute.
7. Unplug the power cord from the electrical outlet.
8. Allow the TV to remain without power for 10 seconds.
9. Plug the power cord back into the electrical outlet.
10. Turn on the TV.
NOTE: The initial setup screen displays if the above procedures were performed correctly.
11. Follow the on-screen instructions to complete the initial set up.
12. Perform a system software (firmware) update.
Thank you for understanding.