The mounting hinge will not raise on my clippers when I push up on the button below the blade

There is a small button at the bottom edge of the blade, push it in and at the same time push the blade teeth away from the clipper. The blade will hinge away from the clipper, you then lift the blade up off the tongue. When fitting another blade pop it onto the tongue, turn the clipper on and snap the blade shut.

The blade release should be under the heel of the blade, just below where the blade tongue hinges. You normally only need to press it when removing the blade, when snapping the blade shut it is mostly not necessary to push it. They are a bit like a door latch that self lock when closing.

ok the blade latch only holds the blade into place.

the hinge assembly which the latch sits behind needs to be open, there is a silver piece with two ridges on, place a flat bladed screwdriver behind the hinge and this will lever open you can then slot the blade onto the hinge and close shut with the clipper running.

There is a picture of an oster clipper in the picture so I assume you are talking about an A5 style blade/clipper. Hold the clipper with the hinge facing you, if the hinge is open, then turn the blade so the blade number is facing up and slide it onto the open hinge, start the clipper and push the blade down to shut it. If the hinge is not open, prize it open with a flat head screwdriver. www.sheaeaseltd.com

With the hinge of the clipper facing you:
Make sure hinge is open, if it is not, prize it open with a flat head screwdriver.
Slide the blade on with the blade siz/number faceing you.
Snap shut.
If this fails, try again, but push the latch in as you snap them shut.
If this fails, you may need repair!
www.sheareaseltd.com

The A5 clipper should have a locking hinge the hinge should be open and slide the clipper blade onto the hinge, now push on the clipper blade bachward and it will snap on. if you don't hear a snap sound the hinge on the clipper maybe worn out and don't have no spring tension.

start the clippers then slide the blade onto the tongue of the hinge assembly , now push the blade into the clipper don't be afraid sometimes they can be tight from new,
Just make sure the two screws either side of the hinge are tight.

Are you sure you have Andis A5 or did you mean Oster A5 Clipper, if this clipper is A5 Clipper, You need to check the Lever for wear, The front of the Lever show wear on both side, Like white color and is not squad this Lever is worn. Need to replace. This Lever moves the blade side to side fully. if the Lever is worn the blade will not move fully side to side and the cutter blade the smaller blade will stay in the middle with hardly no travel to side to side and will not cut the hair even if you purchase new blades. Also I would like to mention if the Oster Locking Hinge is worn out and don't have the require tension to hold the blade in place the blade will not cut. How do you test the Oster Hinge on a Oster A5 Clipper,
(1) first close the hinge, in close potion with your finger nail try to open the Hinge, if the hinge slightly open or opens loose the Hinge is worn. if the Hinge is good it will not open or move and your nail may just brake your nail.
Many of my customers run into this type of problem, and the problem can be solve easily by checking these parts first.
One more item I would mention here if replace the A5 Hinge make sure you get the A5 Hinge not the Oster 76 Hinge they are driferrent, The A5 Hinge has on the back two wire's sticking out that fit on the Oster Latch for the A5 Hinge, the Oster 76 Hinge would not have these wire's on the back. I recommend replacing the Latch when you replace the Hinge. I hope this helps any body that have a A5 Oster clipper or A Oster 76 Clipper.
I have over 20 years in the repair business of Sharpening & Clipper repair. Mannys Sharpening 323 263-4697

Oster Hinge

A5 Latch

It sounds like you may have a bent hinge which is what the blade slides onto. Please call Andis customer service at 1-800-558-9441 to speak with a customer service rep. They can give you instructions on where to purchase a new hinge or send or clippers in for repair.

Thank you,