Problem with EOS Utility

Did you first install the software on the computer, before you connected the camera to the USB connector? It is needed, so the computer knows what to say to the camera. Only then the camera can communicate with the computer.
Software, came on a cd with the camera, or they gave you a link where to download the software.

Consider NOT connecting your camera to your computer.

The best way to download pictures from your camera to your computer involves removing the memory card from the camera and plugging it into a card reader (either built-in to the computer or connected via USB or FireWire). This is likely to be faster than connecting the camera to the computer, and won't run down your camera's batteries.

Once the card is plugged in, it will appear to your computer as a removable drive. You can use the operating system's drag&drop facility to copy pictures from the card to the computer's hard drive, the same way you copy any other files. Or you can use any photo cataloging program.

http://www.usa.canon.com/cusa/support/consumer/eos_slr_camera_systems/eos_digital_slr_cameras/eos_50d#ServiceAndSupport
The above is the support page for your 50d camera.

I could not find a 'black' or 'blank' screen problem and solution in the FAQ's.

So, I think that it should be serviced by CanonUSA.com:
http://www.usa.canon.com/cusa/online_repair_tracking/consumer/eos_slr_camera_systems/eos_digital_slr_cameras/eos_50d?pageKeyCode=requestRepair

Uh.. actually it would be the manual for 50D in English not Powershot A51 that he wants to get. You may download it here:
Canon 50D Manual in English

download "EOS Utility" for the Mac from USA.Canon.com website or just use a card reader.

open device manager, connect camera, it will be seen briefly with yellow triangle and exclamation mark. open it up and uninstall.
Disconnect camera and close windows down. Restart windows, connect camera and switch on, windows will then find it and install driver. Took me hours to figure this one out

Yes, you need to install the SX100 driver software as well. I wouldn't overwrite older versions of the Canon software, though, so do a selective install if you can.

You need to download the Adobe camera raw plug-in for the EOS-50D from their web site, I don't know if the 50D plug-in is available for CS3, it wasn't for CS2,

Try updating the Zoombrowser software.

If you have a connection to the camera, go into my computer and get images directly off the camera using scanner and camera wizard, microsoft's default program. This will at least allow you to transfer your images until you can resolve the software problem.

If you have no connection to the camera via your computer, you need to try some other troubleshooting steps to get a connection. I will post those below in the next post.

hey found solution,

in Menu > Go to the last setting menu > Communication > and set it to PC Connection

hope this helps!