Television and Home Theater

Need help with my 1999 Hitachi big screen TV ...

When I tun it on, sometimes it gives me a smaller, oval shaped picture, which sometimes flashes on and of, and sometimes there's no picture at all for a while.

After some time, the TV usually comes back to the full screen sized image being presented.

What's going on?

What can I possibly do to fix it?

Thanks for any help you can offer!

I have a sony model kv36xbr400 set mfg. date of 9/2000. It doesnt want to turn on. I have unplugged the set for 1 hour and it does the same thing. I can hear the set try to come on but I have no audio or video. After letting it sit for 1 hour I turn it on and I can hear the click and hv try to come on but doesnt. I get 7 flashes on the standby led. Any suggestions.
Thank you,
David

Snowy picture. changed tuner board and resistors in main chassis. need help please.