I've connected my laptop to my 52" sony bravia before and everything worked fine. Recently friend changed my desktop background and then knocked s-video connection lose and when i reconnected i keep getting "invalid format" on my tv. Sounds works since i'm using separate audio cable but S-video no longer works. Changed cables and same issue.

You have to set the playback device on your Vaio to the TV instead of the laptop. You can do this in the Windows control panel under "Sound"

Try a new or known to be good cable.
Try attaching to a different computer.
Prove the monitor will work first.

HI DEAR
ITS PANEL INTERNAL PROBLUM AND YOU MUST CHANG THE PANEL
THANKS
M NASIR

Check all the flat cable connections from T'Con board to panel, for loose connections. Re-seat them all.

It sounds like your set needs servicing. Are the other inputs working? HDMI port failures are indicative of a problem with the main board.

if you constantly change between one type of unit to another. say between your ps3 and another type of device then you could have worn the connector on the hdmi socket. it may need to be replaced. thats the best I can do. we have a bravia but dont change connections at all because it can cause many issues over extend use especially if youre changing devices whilst the set is on, as this can interfere and damage the internal circutry which may have shorted out the hdmi circuits.

OK so its software problem? But how did you solve it?! Thansk!!

Most likely this is caused by a defective main board. Changing the main board will fix the issue about 95% of the time.

To be absolutely sure, the voltages need to be checked on the power supply. If they are not the values listed in the service manual, then you should replace the power supply instead (accounts for the other 5% of the time).

try checking your connectors on the back,if your using hdmi,try scart,if your using scart change the lead or try tv on component connection.

You could see if they will exchange just the unit and save both of you the hastle of checking and repackingit all. It does sound like the unit is faulty.
Or if your Bravia has more than one HDMI input then try on another, or a friends tv if you know some one with a HDMI tv in working order.