My microscope is focused on an object on the slide but not the object I am to observe. What is the possible problem?

dont know the model but it sounds like you have a problem with the light source, Is there a sub-stage condenser?. Try googling
"set up microscope lighting" If the mirror has 2 sides, concave and flat use the flat-plane side. dont point the mirror at an outside sky but rather at a lit pale coloured wall, piece of paper etc.
as a rough start try a piece of white tissue/toilet paper under the
slide and investigate full focus movement ...carefully!!
be careful the the objective stays well clear of the slide.
start with the lowest magnification first. good luck

Your eyepiece (objective lens) is out of focus.

Since there's only a very small amount of light reaching the lens system of microscopes when on high powers, A special technique (called >>>oil immersion
Not using this technique must be the cause of the problem you are experiencing.
eHow will guide you through the exact procedure of using the oil immersion technique: http://www.ehow.com/how_8431358_focus-high-power-objective-microscope.html
Good luck in exploring the micro world!

Compound Microscope

• Compound microscopes can be found in most biology and science classrooms. They are electrically operated and use light to enhance the image of a cell. They will have multiple lenses for viewing.
  

Dissecting Microscope

• Dissecting microscopes are also known as stereo microscopes. They have low magnification and are also light powered. These microscopes can view objects larger than what a compound microscope is able to handle, in three dimensions.
  

SEM

• A Scanning Electron Microscope uses electrons instead of light to create an image. These microscopes produce three-dimensional images with high resolution and magnification. They also have a larger depth of focus.
  

TEM

• Transmission Electron Microscopes use electrons instead of light to create an image. The material prepared must be very thin. The beams of electrons that pass through it give the viewer high magnification and resolution. These give two-dimensional images.
  

There is probably oil on the outside of the object. You can try cleaning it off with some alcohol and a que-tip. If that doesn't work, the seal of the objective has probably failed and oil has seeped up inside. Otherwise the other problem that can cause it is to many small scratches to the outer lens of the objective. This can happen when the objective lens crashes through a slide.

One thing you can do to protect your objective from this happening, is that most microscopes have some sort of up stop lock, which is designed to prevent the stage from coming past a certain point. On your model, this is most likely a screw that sits just behind the stage.

If the cleaning doesn't work, the usually replacing it is the most economical option. This model has a pretty standard object type, so any object that has a 160mm tube length and has standard RMS threading should work with it just fine.

You will need to focus in on the slide. There should be 2 1" diameter knobs on either side of the stand, and just to the rear. Those knobs control the height of the stage (where you slide sits). Slowly raise or lower while looking into the eyepiece. At some point something should be see, if the microscope is working properly.

Sometimes it is easiest to start with the lowest magnification. On the outside of the objective (little lenses hanging down that can be rotated) there should be some numbers written on them (usually 4, 10, 40). Those numbers reference your magnification. If you multiply that number by the eyepiece (10) magnification, you will get your total magnification, so start out with your 4x. It will give you the largest field of view, so it is great for finding whatever it is that you are looking for on your slide. It is also the easiest one to get focused. The higher you go in magnification, the smaller the field of view, thereby the more difficult it is focus in on your sample.

The knob you are talking about is called the x-axis control knob. It does not directly affect the focus. What affects the focus is the slight manipulation of the stage and or slide while you are adjusting the x-axis control knob. It only takes the slightest pressure to throw the focus off very far. Theoretically you could completely remove the specimen holder and move the slide around with your fingers.
The specimen holder may need to be replaced but without further more detailed knowledge of the mechanical problem I cannot instruct further.

There are two reasons. One reason is that when on high power you are working so close to the glass slide that it is easy to misjudge how much you are moving the specimen toward the lens that you can break a slide before you realize it. The coarse focus moves the stage with the specimen on it very fast and you only have a very very short distance within the focus plane before you run the objective lens into the slide.
Secondly, it is just harder to control the minute adjustments needed at the higher powers with the "coarse" focus knob. If you start at the low magnifications find what you want to concentrate on with the coarse focus knobs and then work your way up to the higher powers, you will have very little trouble moving to the fine focus controls at 40x and 100x while still having control of your image.

There is what is called a "stage stop" screw. Its purpose is to limit the specimen from rising high enough to contact the objective lens. The "stage stop" screw is directly behind the black stage platform in plain sight and very easy to access. It is a thumb screw and sits vertically. Simply loosen it a bit to allow the specimen to rise high enough to focus.

If your stage is still in its correct orientation then make sure your objective lenses are screwed in tight as well as the eye piece being secured correctly. Try using different objectives (don't go too high or you may damage your lenses if you ram it into your specimen) and using the fine and course focus. If the you still cant focus using different objectives it's quite possible that your mirrors or lenses inside the microscope have been knocked loose. I would then recommend only having it repaired by a certified microscope technician. If it is still under warranty take it back to the store of purchase or send it back to the manufacturer.