Computer to Tv..HDMI..Problems

[dolomite41]

I recently bought a laptop with an HDMI output...The first thing I did was hook it up to my HD Tv. Right away it worked without any problems and it looked great. Well, now Ive tried to hook it up again and it wont come up on the screen (expect for one time, I struggled trying to get it on...turned off the tv...restart the computer and so on). Ive tried several times to get it to work, but it just shows me a blank screen.

I have a phillips HDTV LCD and a Sony Vaio...any help would be great.

Thanks