I cannot change the aspect ratio on the TV. When I go to the menu, Aspect Ratio is in red and I cannot select it. On certain channels the screen is too big and I can't see the edges of the broadcatsed image.

You can change how your tv displays in the video setting menu under display. You will have a choice between 4:3, 16:9, 16:10, cinema or automatic. I think to fill your screen the best you should choose 16:10 but this is not going to guarantee that all channels will fill the screen. It still has to do with how it is being broadcast to you.

get the on screen menu on the screen
scroll around till you see aspect ratio and click on that use the buttons to change ( you will see the changes on the screen)
click ok and exit when satisfied
Fir aspect ration to change there can be a few reasons
some tv stations produce movies in the wrong ratio and it shows up for the movie as black edges or tall figures or fat figures ( change channel to verify)
or there can be a fault occurring in the board of the set that will not hold preset aspect ratios

If by "nasty wide horizontal lines" you mean LETTERBOX masks (at the top and bottom of the screen), all you need to do is select the correct ASPECT RATIO for the program you are watching. Consult your USER MANUAL to determine the menu settings for ASPECT RATIO.
If you do not understand what "aspect ratio" means, or what different aspect ratios exist, do an Internet search for "aspect ratio" and read.

Go to the picture menu and select a different aspect ratio. Auto sizing is useful as the TV will detect the picture size and select the correct aspect ratio, except for letterbox and super wide screen of course as your screen is not the right shape for those.
Hope this helps.

A DLP Lamp will fail in two ways. 1.The glass tube housing the filament will shatter and the TV will not turn on. 2. The lamp has many hours of use on it and will gradually grow dimmer. At no time will the lamp cause any picture defect. Check your Cable or Sat box for the correct aspect ratio as well as the TV aspect ratio. Chances are the aspect ratio in either system is set incorrectly. If the gray borders are uniform then the aspect ratio is not set properly. If this occurs on certain channels but not others then the particular channel is broadcasting in the 4:3 aspect ratio and there is nothing wrong with your set.

You cannot change aspect ratio when recieving HD signal. Try changing the cable box or satellite box format or aspect ratio.

Aspect Ratio–Selects the screen aspect ratio: Normal, Wide, Zoom, or
Cinema. You can also press the ZOOM button to select the aspect ratio.

The aspect ratio on your DVD player is not set correctly. Look for a SETUP button on the remote control, there should be something like "QUICK SETUP" or something similar on the setup menu, if not then go to the menu that has the aspect ratio settings listed. Change your aspect ratio to 16:9 WIDESCREEN, and this should solve your problem. Your aspect ratio is 4:3 which is for a regular TV, if the images (especially people) look real skinny and tall on your TV then your aspect ratio is not properly set. Good luck to you!

you may want to try changing the aspect ratio on the HD box and the DVD as opposed to the receiver. This should do the thing

You may have a vertical circuit problem causing the picture to stretch out. This is called "over scan". You need to have a tech check it for you. Stargazer