No full hd on full hd TV o_O

We just bought a 42'' Sharp Tv. and i wanted to hook up my xbox 360. The thing was, that i could only play on the normal 420P, while my tv supports 1080P. i tried to switch on the HD-thingy on the cable, but when i tried that the Xbox restarted with a black screen with only audio. any suggestions on how i can solve this? because i want to get the max out of my tv :P tv:42'' Sharp LC-42XL2E No full hd on full hd TV o_O
Do you have the component cables connected correctly?EDIT:Sorry I know a lot of people who have this ''problem.'' Make sure your cable is switched to hdtv, Then when your xbox turns on, go all the way to the right blade select video settings and then there should be an hd settings. You have to manually set it to 1080 it doesn't do it automatically.No full hd on full hd TV o_O
When you flip the switch it goes to sd, which uses the same two plugs for sound but just the yellow for video (which is not plugged in.)
[QUOTE=''tdavis20050'']Do you have the component cables connected correctly?EDIT:Sorry I know a lot of people who have this ''problem.'' Make sure your cable is switched to hdtv, Then when your xbox turns on, go all the way to the right blade select video settings and then there should be an hd settings. You have to manually set it to 1080 it doesn't do it automatically.[/QUOTE]The problem is, when i try to switch to HDTV, and when the xbox turns on i only get sound and no video.EDIT:I also tried it without the yellow cable, but that doesnt work either. So i have the green/blue/red ones in.. the red and white ones in the audio. that should do it right? but nooooo.. i get a black screen :P
420p is hd, you just need to manually change the settings. Do whatever you did to have the video show up, then go to the options and change it to 1080p.
Then i get a black screen. but i am very positive that my tv supports the higher ones, instead of just 480p. And the switch is set to sd for the 480 i think. ah well, ill just google a bit more and look for answers. suggestions are welcome though ;)
If you have the g/b/r connected, the switch position where you get a black screen is sd, if you can see, then it is in hd. just go to where you can see, and then go to the options and change it to 1080p.
Nevermind, stupid stupid stupid of me.. i got it working now. The audio was in the XTR3 while the video was in the XTR8. xD sorry, this was a bit stupid... still, thank you for your replies. i appreciate it :)