Since you recently replaced your hard drive, I'm betting you had to reinstall some softwares, too. If so, you have several possibilities...
1. Be sure your operating system (Windows 7) is up to date. If it's an earlier version, it may lack the drivers to support your particular camera.
2. Reinstall the Canon software that came with your camera on a disk (or download the latest version from the Canon website). These include EOS Utilities, which allows the computer to recognize and work with the camera.
3. Use a card reader instead of connecting the camera itself, then working within Windows Explorer...
a. Set up a folder to receive the downloaded images.
b. Open up the memory card, which will appear like another drive, probably labelled EOS_DIGITAL G:, or similar.
c. Open the DCIM folder
d. Open the 100EOSxx folder (there also may be 101EOSxx, 102EOSxx, etc. folders, camera will create a new one every 9999 images)
e. Click on any one of the image files found there, then press Ctrl, a. This will highlight all the files in the folder.
f. Then drag and drop the image files as a group to the destination folder you set up earlier.
It takes a lot longer to write and read this, than it does to do it! It's really quite easy, once you've done it a time or two. If you left-click/held to do the drag and drop, images will simply be copied. If you instead right-click/held the drag and drop, you'll get a menu that asks if you want to move or copy the files. I'd recommend just copy for now, just in case the download is interrupted or something else occurs. Later, once you are sure the download was successful, you can simply format the memory card in your camera to "erase" the images on it. (Note: Formatting doesn't actually erase them. It just marks them as okay to be overwritten. After in-camera formatting, until you start shooting and overwriting them, those old files actually can still be recovered in an emergency.)
You still may need to update your OS and/or other software on your computer, in order to work with the files you just downloaded.