I am trying to connect my computer Sony Viao vgn-sz780 to my Samsung TV pn42a450p1d via a VGA cable. It worked one time before but when I repeat the steps to do it again it doesn't work. I can get my TV to have a PC source but it keeps saying "check signal cable" or "no signal." I have installed all the updates for my laptop and I also have tried changing the external display detection setting (that is what worked last time, but this time when I do it the TV just switches from "check signal cable" to "no signal") I have also tried changing the monitors under the display settings and identifying a second monitor and then checking the box "extend destop on to this monitor" However it keeps reverting back to the normal settings and does not allow the box to remain checked after I press Apply. I also have the right refresh rate and display setting for the TV so that can't be the issue...

Any ideas?

Be sure Tv is selecting PC for an input, If vista, press the windows + X. This should bring up Windows Mobility Center. Then press connect display.