The problem of the erratic mouse has been around for some time. Having personally experienced this fault, I know it can be one of the most puzzling and frustrating problems.
In my experience, there are five unrelated causes to this problem. The difficulty comes when trying to work out what is the issue for you. If you get it wrong, the prospect is that you will add a new cause rather than solve your problem.
The best way to proceed is as follows:
1) Your mouse might actually be faulty (though this is rare). Or, it may be dirty so that the trackball does not run smoothly or the optical window is blurred, depending upon the type of mouse you have. The best way to eliminate the mouse itself is to try it on another PC.
2) If you have an Optical mouse (one with light emitting from it’s base), then the absolutely most common cause of erratic movement will be your Mouse Pad or the surface that you have the mouse on. Almost any surface can cause the light refraction to be uneven and confuse the mouse as to the direction of movement. The mouse may not even need to be moved for this to occur. Simple vibration in the environment can be enough to cause a light shift to which the mouse will respond. So always start treating the erratic mouse fault by using a velvet finish, dark coloured mouse mat. These are usually the cheapest you can buy and have the best light response characteristics.
3) Once you have the correct mouse pad, if the problem persists, then you need to check your BIOS settings. Some BIOS allow for a USB mouse. I don’t know what this setting does, except that if set incorrectly it can cause the erratic mouse problem. I suspect the reason may be due to a timing of the interrupt for the USB port; as a mouse is an always-on device whereas many USB devices are temporary attached or intermittent use.
4) Are you sure you did the above? This third step should only rarely be required and can make the previous two causes worse thus making your fix harder to achieve. Go to: START/CONTROL PANEL/MOUSE/HARDWARE/PROPERTIES/ADVANCED SETTINGS/SAMPLE RATE Set the rate lower than already shown and whilst on the way through make sure that the mouse installed is what you have (There is also a listing for HID compliant mouse. Ignore this as it is a system interface protocol driver used by windows to map the mouse hardware to the desktop via USB.) Really you should not need to be here at all. So are you absolutely sure you did steps 1 and 2.
5) Still not working, then you are in some difficult territory. Make some careful observations. If the problem occurs when you have multiple instances of your Internet browser or other multiple programs open, then I have found that this arises when you shift focus, or close a window. In this case, the issue is memory displacement and management and there is no fix that I am aware of. However, this fault is very rare and not persistent even when it is a factor. At least you will not have to put up with it often.