My Canon 10D will not Power On. Do I need the original battery ? Currently I have A battery from my Canon 30D in the 10D.

To purchase a battery door for your D10, go to eBay and search for "10D battery door." You will see several for sale and they run around $7.00.

Hope that helps,
BAX

One side of the reverse adapter has a 67mm thread, the other side has a lens mount. Mount it to the camera body as if it were a lens. Bear in mind that it's intended to screw onto the front of a lens and then mounted onto a camera to put the lens onto the camera in a "backward" position.

Refer to my answer to your other post.

You may download a copy of the AE-1 manual here.
If you have an AE-1 Program, you may download its manual here.

In your set up menu there is a function that will allow the camera to auto power off. Normally this has several setting from a few seconds to several minutes. My first thought is that this has been altered and the camera has been set to power off in a few seconds.

Try cleaning your battery terminals. You can use a little rubbing alcohol on a q-tip. If you are still having issues then you will need to get another battery as that battery is shot

Yes, it is normal. This is a reasonably old DSLR, and it's designed for you to look through the viewfinder (it's more accurate anyway as it's looking through the lens). You'll find if you keep one hand under the lens and one hand on the shutter, it'll feel quite comfortable to look through the viewfinder.

You can still view photos you've taken after you've taken them though.

A more appropriate product is Suntax DRF14C for Canon 10D, 30D.
http://www.suntax.com.sg/DRF14.html

I seem to recall hearing that the power switch can be a problem on the 30D .. I'm not going to suggest you take it apart to clean the contacts .. better go to a Canon Dealer I think ..

Is the lens a Canon EF or EF-S lens? Have you used it before on this particular camera body? Did you do anything else (change memory cards, etc.) at the same time you changed the lens?

Try taking off the lens and cleaning the electrical (metal) contacts on both the lens and the body with a small dust-free cloth or pencil eraser. If that doesn't help, switch in the lens you were using before. If it works with the original lens, there may be an electrical problem with the other one. If it no longer works with the original lens, you may need to have it serviced.