Good Picture but problems after a week

I recently bought this product at Circuit City on Black Friday. Waited in line for 3 hours and picked up the 46 inch sharp aqueos. I brought it home and it worked for a week and then the screen went black and a loud high pitch screeching sound came from the TV. I will be looking to return it. The picture is fine with the computer monitor input and probably the HDMI (didn't use HDMI). However, with the RCA cables (Red White Yellow), the high pitch sound comes alive and there is no picture. The TV worked fine for 6 days then this problem occurred. I have tried turning it off and on again with the same problem happening with RCA inputs 1 thru 3. I plan on returning the product and getting another one. Hopefully this problem is not on all of these models. The picture did work well with my Nintendo WII for the first 6 days, but now I can't get a picture from it, just the high pitch screeching sound (very frustrating)! Also the picture wasn't as good as I had hoped from my satellite receiver. But that is because I didn't have a high def receiver. Now I need to buy a high def Sat Receiver and high def DVD player that will support 1080P. More money I wasn't anticipating spending.