400D LCD Display not working

Hope someone here can help me, I turned on my 400D last night and had no display at all from the rear LCD. If I turn the camera on the green light comes on and stays on even after I switch the camera off. If I turn it on again and switch it off again right away camera will switch off. I have tried taking out both batteries and letting the camera reset and still no display. I have tried three different batteries, different compact flash cards, different lenses all with the same result. The camera was working fine when I put it away about a month ago. The next thing I have been thinking of try is a new 2016 battery. The camera will still take pictures and the lens will focus, flash will work but still no display. Camera is no longer under warranty so I am hoping to see if there is a fix so I don't have to send it back. Depending on the cost I don't know if I would or not as I also have my 40D, but the Rebel probably has less than 2000 clicks on it.

Thanks In Advance
Wayne

I assume you had the backup battery out, as you talk about removing both batteries? But whether it's new or not shouldn't really matter, as the camera can work with the main battery only, except for keeping time correct.

Yes had the backup battery out, just can't figure out what is causing the problem.

My 400D LCD cuts out randomly and I just tap (or sometimes slap) the LCD and it starts working. I have a couple of other random issues with this camera and out of warranty also, but makes a great backup camera. Mine has been like this for about 9 months, but I have learnt to live with it. Now my new camera has finally arrived I will send back to Canon service.

It may work with the main battery only, but it needs the button battery to keep the flash memory from wiping. Once the button battery get's too low, turning off the camera will wipe the flash chips every time and you will have to start over. I'd replace that battery and give it a try before going any further. It still may be something else, but at least you eliminated one of the more probable causes.