350d canon, mirror flicking up and down when power is off

1.Remove the battery, lens and CF card. Allow the camera to sit without power for 20 minutes and then reinsert a fully charged battery.
2.Turn the camera on and push the shutter button as if you were taking a picture.
3. If you don't get the error message reattach the lens and insert the CF card.
4. Check the below canon eos 350d service manual link:
http://goo.gl/ELh523

it will help you to save a lot of money
Hope it helps, Thanks

Shutter Assy, Mirror Assy or Shutter Button taken a coffee breaks.

You did try using a new battery?
Or your battery is not over 3 years old?

If I can help, just send me an email.
[email protected]

I'm not sure what you have done to obtain this screen but I'm including the instructions of how to do a camera reset which will bring the camera back to factory default settings.

Diagram

Hello hemantp. This error code in this model indicates that the lens electrical contacts are dirty or slightly oxidized. To clean them you will need a common pencil with a clean eraser on the end and a lens cloth.

Detach the lens from the camera and hold it so that the lens' gold contacts are pointing down. Lightly "erase" their exposed surfaces and then clean them with the lens cloth to remove any debris.

Do the same with the gold contacts inside the camera body. Although this is a wee bit more challenging, you can do it by holding the camera so that the lens opening points down. That way no debris will fall inside as you clean. Joe

It is due to some kind of electrical contact failure.
For more details and common causes of Err 99 read the following article:
http://www.lensrentals.com/news/2008.12.31/canon-err99

It maybe the case your mirror is stuck in the up position. Take the lens off and see if the mirror is lodged in its up position. If it is stuck get it repaired by a Canon technician

belie e this is a flash error. will not pop up or blocked.

Have you tried his battery pack in your camera??? if it still does not work your camera probably blew a fuse and repair cost run about 180.00 to repair it. If you need any further help please fell free to ask.

The first thing to check is that the card door and battery door are firmly closed - press on them while the camera is on to see if it powers up. If not, there's probably a blown fuse - it will have to go to the shop.

This is a board comonent failure as you surmised. I doubt id parts are available- it will be a complete replacement board. Check the Canon Support for a repair estimate.