ISO stays on Auto. I push the ISO button to change the ISO off of Auto and it doesn't do anything on my 40D

Try pushing the menu button and selecting "shooting menu". There you should find options for: Image Mode, Whire Balance, Continuous Shooting, ISO, and Color options.
Setting the White Balance to "Auto" actually produces the most accurate and reliable results.

Sound like a problem with the CCD Image sensor go to bad. In both cases this isn't a job that you could solve yourself; this wrong include distorted images or abnormal colors, scratchy purple lines, blank or black pictures, and/or black videos with good sound being recorded on the camera's flash card.

I suggest check THIS LINK for additional details in this previous solutions for an Defective CCD (Charge Coupled Device) and next contact your Canon service. I strongly suggest (taking into consideration the age of your camera) to evaluate the cost of repair versus the cost of a new camera with similar features, before making a final desicion.

Hope this helps.

Yes you need to change the white balance (WB). If the pix are yellow it is because the white balance is set to daylight and you are shooting under tungsten(orange) and/or fluorescent (bluey green).
Try the WB in auto but sometimes auto doesn't work perfectly, or if shooting under tungsten only change to tungsten etc
If you want to be sure to get the correct balance shoot a white card slightly underexposed and correct it afterwards in whatever photo software you use.
The blurry is caused by too low a shutter speed but if already at 1600 iso you cant go much higher without running into noise problems so use a flash gun on auto.
I hope I have been of help but please do not hesitate to ask if you have any further questions.

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In the Basic Zone modes, you don't. The camera automatically sets the ISO in the range 100-800.

In the Creative Zone modes (P, Tv, Av, M, and A-DEP), press the ISO/Flash Exposure Compensation button (rightmost button in front of the top LCD panel). This will display the current setting on the top panel. While looking at the top panel or in the viewfinder, turn the command main dial (just behind the shutter release button) to change it.

In manual mode the light meter result is the output of setting the apeture and shutter speed. It will constantly change as you change these and the ISO until you get the desired exposure. Is this what you mean by inconsistent? If it is giving verying results in the same conditions try it with ISO 100. That should fix it

Your Highlight Tone Priority is turned ON. Once ON, all your zeros will be replaced by the letter 'o' to remind you that it is ON. If I remember correctly, the ISO range is limited too.

You can change the ISO setting also to Auto. If you have the advanced guide (see pp 80, 107).
Press the ISO button it will switch from various ISO setting to AUTO.

Do remember in Bright light , a lower ISO number like 80 will give you very fine images, while as the light level goes down, the ISO number will change to a higher number and the image will become more grainer.
I hope I could answer to your query.
Please do rate. Thanks

Check if your Highlight Tone Priority is turned ON. Once ON, the ISO is limited to between 200 and 1600 until you disable Highlight Tone Priority. Also, all your zeros will be replaced by the letter 'o' to remind you that it is ON (Eg 2oo instead of 200)

Same problem. Fully charged main battery. In my case, I hadn't used the camera in over 6 months. All I did was pull the main battery and then pulled the small CR 2016 button cell battery located inside the main battery compartment and re-inserted both batteries. The camera made a quiet click and then turned on with the main power switch and asked to reset the date and time. Works fine now. If this doesn't work just purchase a new button cell.

Were you indoors? if so, take the ISO of AUTO and out it on 400. Leave the camera set like you had it, Manual 1/60 @ 5.6. Do notuse evaluative metering. Use single spot metering or the smallest center weight setting.