I've had this upscaling dvd for a few months now and i have never been able to get it to work using 720p or 1080i

- can anybody help? It plays dvd's with no problem at 576p so i know there is nothing wrong with the HDMi cable or the tv.
When i change the setting to either 720 or 1080 the screen changes to 'snow' - i have tried to adjust the other settings in the menu and this does not seem to do anything either

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I took a long look at it today and the output given on my tv does appear to be correct (either 720 or 1080) but the screen is completely blank or fuzzy...when i change back to 576 it is fine. I also tried adjusting all the other possible display settings (in every possible way) and the result was always the same, very frustrating.
I also use an xbox 360 with component cable which is perfect at HD resolutions....my tv is a Philips 32PF9631.
If anybody has any suggestions i would be grateful, i'm reluctant to buy another player but i'd like to know if its a faulty dvd player (or maybe something else?)
Mike.