I have a SE13 HD projector connected to TW S/A Explorer 4250 HDC, running it through a Focus Enhancement Video Processor. The problem is when I attempt to change the Output to 720 or 1080i on the cable box the screen goes blank and I can't get the HD channels. The output on the processor is 720i. What am I doing wrong? Help!!!

After a quick Google, I have no idea what an "SE13" is nor can I tell why the h*** you would want to use a "Focus Enhancement Video Processor".

Assume you've tried plugging the cable STB directly to the projector, (which should be HD capable,) either with YPbPr cables or HDMI and get HD okay. The cable STB has to be set up for 1080i or 720p output, and you have to be subscribed to or just receiving HD. If an added video processor then blocks HD, something's set wrong on the VP or it's malfunctioning. Maybe it's just a typo, but the VP should output 720p for HD, not 720i. Sometimes added video processing steps can worsen HD or SD PQ. -- John

There is zero reason to use a video processor with HD. As suggested, connect the HD box directly to the projector, and you are done.