I used the directions someone gave but still cannot find the dirty spots..

I'm sure you've either finished the game or thrown it out the window in a fit of pique by now, but here's what I have just found about the "dirty spots".

There are 3. Keep cleaning an area until you see a little puff (like dust) into the air at each spot.
1: the lower of the 2 swords hanging horizontally on the back wall near the top. You'll see the reddish stuff on the blade. That's what you need to clean.
2: the "wing" extending (toward the center of the overall image) from the samurai helmet on the right edge, in front of the window. It looks kind of gray to start with. Rub until you see the puff of dust into the air.
3: the middle of the 3 large spear tips in the right foreground. It's long and skinny and also reddish. As you clean it the red comes off.

It's the 3rd one that gave me trouble. I thought I had it clean...it all looked "white". But nothing happened. I started the whole level over. Came to the same point and found that I hadn't cleaned that spear tip to the "puff of dust" point. Be sure you go all the way to the very tip and beyond.

Once I got the puff of dust from the 3rd site, the game continued on.