Hi some fungus have appeared on the rear elements of my canon 100mm f/2.8 is usm macro lens . ive been looking everywhere for a video or manual of how to remove the rear elements :(

Your 100mm lens autofocus not working.it may be due to autofocus flex cable inside the lens damaged. It is replaceable part. You may have to contact service technician. However when you switch to manual mode it should focus & click. Try it.

It seems that you have either a faulty lens or one which is performing outside of the minimum quality standards. You have clearly done everything possible to try and eliminate all other causes. Looking at the firmware updates for your camera, none of them mention an issue involving your lens but you may wish to ensure that you have the latest firmware anyway.

All you can do is to contact Canon customer care to request that the lens is exchanged.

I had a similar situation with a 100mm macro. I used the Canaon US site and comunicated via the internet and they sent me a pdf of the manual. "Service and support, support by email."
http://www.usa.canon.com/cusa/consumer/products/cameras/ef_lens_lineup/ef_24_105mm_f_4l_is_usm#ServiceAndSupport

you should be able to use that lens with it. As long as it attaches to the SLR body ok. The thing to be aware of is with better technology in the newer camera you may have AF issues with that particular lens.

Put the macro adapter on the camera and move the camera in and out from an object to try to focus the object in the display. Remember, macro is very small, very close and very small field-of-focus. I hope this helps.

You can TRY to see if the screws are loose on the back of the camera around the rear element.  Sometimes they look flush but need a couple of gentle turns to bring everything where it should be.  If possible you should use a JIS (Japanese Industrial Standard) Phillips screwdriver so you don't strip the screwdriver head.  Don't use too much force - these are precision instruments and only need a certain mechanical tightness - too much can cause harm.
Unfortunately, if it's not those rear end screws, you'll have to send it in to Canon.  Fortunately Canon is very good about repairing lenses, even if they are slightly out of warranty.
Good luck

Well it could be used but you may find the auto focus to be too slow and the aperture of f2.8 a bit dark for indoor sports. That lens is best used in the role it was intended — macro photography. Take a look at the 85mm f1.8 USM or the 100 f2 USM. They are reasonably priced and offer greater AF speed and low light ability.

Hope this helps

By the way are these RAW images? What type of lense are you actually using, check this

EOS-1Ds Mark III EOS-1D Mark III EOS-1D Mark II N
EOS-1Ds Mark II EOS-1D Mark II EOS-1Ds
EOS-1D EOS 5D EOS 40D
EOS 30D EOS DIGITAL REBEL XSi/EOS 450D EOS DIGITAL REBEL XTi/EOS 400D DIGITAL
Compatible Lenses
EF 14mm f/2.8L USM EF 28-70mm f/2.8L USM
EF 14mm f/2.8L II USM EF 28-135mm f/3.5-5.6 IS USM
EF 20mm f/2.8 USM EF 28-200mm f/3.5-5.6
EF 24mm f/1.4L USM EF 28-200mm f/3.5-5.6 USM
EF 28mm f/1.8 USM EF 28-300mm f/3.5-5.6L IS USM
EF 35mm f/1.4L USM EF 70-200mm f/2.8L USM
EF 50mm f/1.2L USM EF 70-200mm f/4L USM
EF 50mm f/1.4 USM EF 70-200mm f/2.8L IS USM
EF 85mm f/1.2L USM EF 70-200mm f/4L IS USM
EF 85mm f/1.2L II USM EF 100-400mm f/4.5-5.6L IS USM
EF 100mm f/2.8 Macro USM EF-S 60mm f/2.8 Macro USM
EF 135mm f/2L USM EF-S 10-22mm f/3.5-4.5 USM
EF 180mm f/3.5L Macro USM EF-S 17-55mm f/2.8 IS USM
EF 200mm f/2.8L USM EF-S 17-85mm f/4-5.6 USM
EF 200mm f/2.8L II USM EF-S 18-55mm f/3.5-5.6
EF 16-35mm f/2.8L USM EF-S 18-55mm f/3.5-5.6 II
EF 16-35mm f/2.8L II USM EF-S 18-55mm f/3.5-5.6 USM
EF 17-35mm f/2.8L USM EF-S 18-55mm f/3.5-5.6 II USM
EF 17-40mm f/4L USM EF-S 18-55mm f/3.5-5.6 IS
EF 24-70mm f/2.8L USM EF-S 55-250mm f/4-5.6 IS
EF 24-105mm f/4L IS USM -

A fat rubber band tight enough to stop the barrel movement, but not so tight it restricts manual zooming is the best, extremely effective, low-tech fix for this problem - I have done it for years

The USM focus works by applying pressure to a set of rollers. That pressure is achieved with a large diameter spring washer. It is held in place by another large diameter flat washer that on assembly is rotated 60 degrees to lock it in place. If the lock washer has moved due to mechanical movement (ie rapid manual movement of the focus ring) it could unlock and then all pressure to the USM motor parts and rollers is lost giving the loose feel you mentioned.

You will need to dissassemble the rear of the lens to see the USM motor parts, rollers and locking ring to reattach it. Follow the links at my pbase gallery to see the dissasembly. When I took my lens apart the focus and USM motor went all loose and I wondered how could it work ever!!!. The locking ring was off which sounds just like your fault. http://www.pbase.com/barry_2718/efs1785mm I also have a flex cable cracked which is a much harder fix. Take careful note of the parts (mark then with a felt marking carefully) to achieve a reassembly exactly as removed.