TV 1080P resolution

I bought a Sharp LCD 42" top of the line TV 4 years ago. At that time, the TV was the most technologically up to date model and cost close to $2000.00. The company, Sharp, categorized this TV as "Full 1080P capability." The store where I bought the TV also told me that this TV was fully 1080P capable and that even though, at that time, there were no 1080P broadcasts, by buying this 1080P set now, I would be ready when 1080P came into vogue. I am a DirecTV customer (live in a area where there is no cable). DirectTV offers Pay-Per View movies in 1080P resolution. Why won't my TV recognize their 1080P signal? Sharp says it's DirecTV's fault. DirecTV says it is Sharp's fault since the TV is NOT 1080P capable regardless of what claims they (Sharp) may be making in this regard.

I had DirecTV install a new receiver since Sharp said that had to be the problem (my DirecTV receiver was not 1080P capable). This made no difference. My TV still will not interface with their 1080P signal.

Any ideas here?