I recieved a brand new Canon Rebel XSi in the mail. I throughly read the manual & assembled it carefully by the book. Kept it in all the correct settings. Also kept it in a warm, dry area. I grabbed the camera battery and battery charger, put it into a working outlet & let the battery charge for a few hours, making sure the light turned green. I put the battery in correctly, & there wasn't even a flicker of light or sound. I tried all the trouble shooting mentioned in the manual. & let the battery recharge. It still isn't working. I really don't know what could have gone wrong. Any advice is apprecaited. Thank you.

Try using manual focus. Make sure your auto focus points are correctly set. Look for button that looks like matrix. Press it then use/press joy stick type button to select auto focus point.

One source lists the mirror box assembly for $78.

The EOS 450D is called the Rebel XSi in some parts of the world. You may order an XSi shutter assembly here.

Yes and no. It will work fine as a manual flash, putting the burden of figuring out correct exposure on your shoulders. It will work fine in the automatic modes on a Nikon camera.

Quantaray makes a Canon version of the flash which will work in the automatic modes on the Rebel XSi.

That's what the owner's manual is for.

Most entry level SLR cameras will struggle to focus in low light, especially with the kit lens. By rights the flash should popup and emit a flash pulse to help focus. This is called focus assist. You might have to consult the manual to check if this function is turned on or not.

Create a folder on your desktop. Use the cardreader to download to it.

You will need to read the manual. I f you have a basic understanding of how ISO, shutterspeed & Aperture width combine to determine the 'right exposure.

Try this:
Set the camera to Av (aperture priority mode). Half press the shutter button and see the light meter indicator to see how well exposed your shot will be. For most cases you would be aiming for a value of 0 (properly exposed). The metering mode determines what part of the frame is used to compute the correct amount of light. For starters begin with pattern metering. Try and aim for a shutter speed of 1/125 or more if you are using the 17-55 mm EF-S f3/5-f5.6. Try and shoot at 40 mm F/5.6 (in Av mode this can be set by rotating the dial near the shutter button.
All the best

You need to by one with a Canon EF fitting.

Unless you have a Rebel XSi with "live view", you're not going to see the image on the LCD before you take the picture. No digital SLR made before 2007 had this option. You compose your picture using the optical viewfinder, and only see your picture after you have taken it. (But at least you don't have to wait until the film is developed. ;-) )