Take a pad with rubbing alcohol and rub the ball thoroughly, as there might be some debris and dirt caught under it prohibiting it from moving. Otherwise http://www.mightymouserepair.com has a guide or my personal favorite...

http://shirster.multiply.com/journal/ite...

good luck!

I've had very good luck using a high-nap towel or microfiber cloth and a little cleaning solution to fix this issue:

1. Dampen one section of the towel or cloth with some iKlear, windex, or water. You want a slightly damp area and a dry area.

2. place the towel on a hard level surface, turn the mouse upside down and roll the scroll ball vigorously in all directions for several minutes, alternating between the damp and dry areas.

3. Test for restored function, repeat as necessary.

BTW: I've taken a few completely failed mighty mice apart, but the newer ones have plastic weld tabs on the bottom ring, making it almost impossible to reassemble the device in a working manner - the ring is the gliding contact point for the bottom of the mouse, so it has to be level and firmly attached.

riDerz

nice job, I know you have fixed it, but next time try this:

1. get a thick WHITE paper, thickest you can find

2. put the paper somewhere stable

3. put the scroll ball (gray ball) on it (holding the mouse opposite-down)

4. move it around with pressure in different direction for a minute.

5. SORTED

Unfortunately, you can't disassembly Mighty Mouse without partially destroying it.

As for cleaning - PTR702 and David clearly guides you towards the solution for your one direction scroll.

Or just spray some compressed air at the trackball.

There's an easyer way to clean it without open the mouse.

You just have to turn the mouse upsidedown and move the scroll with a wet finger.

It cleans the dirty inside.

I'll make it so often and it always work,

if you clean it on the white paper you have a good result the first time but you will damage it doing it several times... my old mighty mouse doesn't work because the scrolling ball has damaged a little piece of plastic inside the mouse.

my second mouse works perfectly since 2008 because every 5/6 months i open it and clean the internal parts just with my fingers, without alcohol or other stuffs... every time i need to break the lower side with a cutter but i always fix it with glue when i finish to clean...

one more important thing: i'm not an hygienie maniac but it's better to use the scroll with extremely clean hands... i'm not a doctor but i think that the dirty inside my mouse is my dead skin with dust...

so always clean hands and if you can cover the mouse when not in use...