I loaded the slide tray properly and put the 35mm slides in it properly, when I click scan it will act like its going to scan. Then a minute later a error screen pops up saying either the cover is on it, its not placed properly, or the lamp isn't warmed up. I have had it on 30 min, it will scan documents just fine, but not slides.

When you go to scan your slides, the software should have a setting for "slides", or "negatives". Make sure you select the correct one for what you've put in.

Hi Stanley - does this youtube video help? http://www.youtube.com/watch?v=EcALdbbCnSk
If not, let me know and we can investigate further.
Regards,
Justin.

The whitest white there is is the reflective white on the underside of a scanner tray. Get 2-4 pages of regular office paper and put them between your slides and the scanner lid. That should at least be better. If still not acceptable, try a flat (as in matte, not two-dimensional), white piece of thin cardboard instead of the paper.
Try it and you'll see where I'm going. Does your printer/scanner come with any photo adjustment features in its software?

This multi function printer/scanner cannot scan 35mm slides and negatives.
Some flat bed scanners with a lighr scource that shines through 35 mm slides and negatives can scan them.
You will be better off getting a dedicated 35 mm slide/negative scanner.
Check out this WEB site foe slide scanners.
http://www.google.com.au/#q=35mm+slide+scanner&hl=en&prmd=imvns&source=univ&tbm=shop&tbo=u&sa=X&ei=dYFIUPKBKMSyiQedl4G4DQ&ved=0CEkQrQQ&bav=on.2,or.r_gc.r_pw.r_qf.&fp=4469b7ccc4340a33&biw=1016&bih=535

Your scanner came with some software inside the box. If this is a second hand scanner with no additional software download the drivers from www.canon.com and run the software accordingly.
Mac os X does not require this process. connect the scanner to your machine and simply load the slides in the tray scanner and use the application "IMAGE CAPTURE" located in local_disk/applications/
The pictures automatically load and you select to crop or scan as is.
Later the image will appear on the desktop upon completion of scan.
For windows: I made you a link for your convenience: http://www.usa.canon.com/consumer/controller?act=ModelInfoAct&tabact=DownloadDetailTabAct&fcategoryid=351&modelid=10242

I have successfully used my Visioneer 9520 to scan 35mm slides, and they came out perfect. To do this, in my image editing software, I select File/Import/Acquire/Visioneer ScanManger Pro. This opens the VIsioneer scan manager window, where I select "Scan 35mm using:" and then I choose the desired scanning configuration, e.g., "35mm Better, 35mm Best, Custom" etc. See image below.
BTW: After several moves, I have lost my 35mm scanning template. Do you know where I can get another one, or do you know someone who could actually scan theirs and email the image to me? I could then create a duplicate from heavy black construction paper or card stock.

Here is your products support weblink for you to download an instruction manual for your model:

http://www.usa.canon.com/consumer/controller?act=ModelInfoAct&tabact=SupportDetailTabAct&fcategoryid=235&modelid=10445#DownloadDetailAct

There is a great little device at Bed Bath & Beyond right now that is inexpensive and easy to use. You just pop them in there hit a button and do the next one. There are also 6 extra converter trays for around $20 so you dont have to spend all of your time waiting on one to scan so you can put the other one in. You can find it here http://www.bedbathandbeyond.com/product.asp?order_num=-1&SKU=15800313&RN=2017

In order to scan 35mm slides to your computer, you need a scanner that has the capability of doing this. These scanners will either come with a 35mm adapter that will allow you to scan the slides, or there are scanners that will scan only 35mm slides. A good recommendation is either this or this.

Thanks and please take a moment to rate as fixya.

I've not ever seen "square" 35mm slides. By definition they are a rectangular positive film in an outer square "mount".

If you have a truly square piece of film then it is not a 35mm slide. You may have to use settings other than those for a 35mm film but these would be I don't know.

When were they taken (approximately)? What brand of film? Are they in a cardboard "mount?