The mirror is obviously stuck in the up position when it should be down at any power off. The camera is probably trying to clear the mirror by doing a cycle of the mirror motor.
Before you start trying to disassemble it you might try to gently see if you can get the mirror to release from the up position. It might be as simple as a misalignment issue. Just don't force anything at this point if the mirror looks like it is still aligned squarely at the top of the mirror box.
The shutter curtains also appear to be at the end of exposure position (the first curtain is open and stored at the bottom of the sensor and the second curtain is closed) and need to be reset to the default position of first curtain closed and second curtain stored at the top of the sensor.
I'm pretty sure the 450D does not have a mirror driven by a motor in both directions, but rather uses a spring driven return when released by the mechanism that retains it in the up position. This spring might have become dislodged from its contact points. (Some of Canon's newer upper tier bodies, mostly those with frame rates of 8-10 fps or more do have a mirror that is motor driven in both directions.)
It may wind up being that the motor that drives the shutter has lost its connection with the shutter curtains and the camera won't release the mirror until the shutter curtains have been reset. I'm not sure which must be confirmed first before the camera will proceed with the other: shutter curtain reset or mirror down. It all happens so fast I can't tell from any of my Canon cameras.
One thing you might try is to see if you can get it in Live View mode and see if the second shutter curtain opens. If so and you can take a picture (without a lens you'll need to use M exposure mode), try to watch the shutter curtains to see if they cycle when you press the shutter button. It will be easier if you use a shutter time of several seconds to separate the beginning and end of the sequence. The first curtain should close from the bottom and then reopen to begin the exposure, then the second curtain should close from the top to end the exposure and then reopen back up into the top.