If you are experiencing problems with your mouse, you need to look in only two general places—hardware or software. Because mice are basically simple devices, looking at the hardware takes very little time. Detecting and correcting software problems can take a bit longer, however.

Cleaning Your Mouse

If you notice that the mouse pointer moves across the screen in a jerky fashion, it might be time to clean your mouse. For a mouse with a roller-ball, this jerkiness is caused when dirt and dust become trapped around the mouse's ball-and-roller assembly, thereby restricting its free movement.

From a hardware perspective, the mouse is a simple device, so cleaning it is easy. The first step is to turn the mouse housing over so that you can see the ball on the bottom. Notice that surrounding the ball is an access panel you can open. Sometimes instructions indicate how the panel is to be opened. Remove the panel to see more of the roller ball and the socket in which it rests.

If you turn the mouse back over, the rubber roller ball should fall into your hand. Take a look at the ball. It might be gray or black, but it should have no visible dirt or other contamination. If it does, wash it in soapy water or a mild solvent, such as contact lens cleaner solution or alcohol, and dry it off.

Now take a look at the socket in which the roller ball normally rests. You will see two or three small wheels or bars against which the ball usually rolls. If you see dust or dirt on or around these wheels or bars, you need to clean them. The best way is to use a compressed air duster, which can blow out any dust or dirt.

You also can use some electrical contact cleaner to clean the rollers. Remember, any remaining dirt or dust impedes the movement of the roller ball and results in the mouse not working as it should. Put the mouse back together by inserting the roller ball into the socket and then securely attaching the cover panel.

The mouse should look just as it did before you removed the panel, except that it will be noticeably cleaner. One of the major advantages of the new breed of optical mice is the lack of moving parts. Just wipe away dust from the optical sensor, and that's all the cleaning an optical mouse needs.

Interrupt Conflicts

Interrupts are internal signals used by your computer to indicate when something needs to happen. With a mouse, an interrupt is used whenever the mouse has information to send to the mouse driver. If a conflict occurs and the same interrupt used by the mouse is used by a different device, the mouse will not work properly—if at all.

Interrupt conflicts caused by mice can occur when a serial or PS/2 mouse is used, but not when a USB mouse is used. Mouse ports built in to modern motherboards are almost always set to IRQ12. If your system has a motherboard mouse port, be sure you don't set any other adapter cards to IRQ12; otherwise, a conflict will result.

If you are using a serial mouse, interrupt conflicts typically occur if you add third and fourth serial ports, using either an expansion card or internal serial device, such as a modem.

This happens because in ISA bus systems, the odd-numbered serial ports (1 and 3) usually are configured to use the same interrupts as the even-numbered ports (2 and 4) are; IRQ4 is shared by default between COM1 and COM3, and IRQ 2 is shared by default between COM2 and COM4.

Therefore, if your mouse is connected to COM2 and an internal modem uses COM4, they both might use the same interrupt, and you can't use them at the same time.

Because the mouse generates interrupts only when it is moved, you might find that the modem functions properly until you touch the mouse, at which point the modem is disconnected. Another example is when your system will run properly until you try to go online with your modem; then the conflict usually locks up the system. You might be able to use the mouse and modem at the same time by moving one of them to a different serial port. For instance, if your mouse uses COM1 and the modem still uses COM4, you can use them both simultaneously because odd and even ports use different interrupts.

The best way around these interrupt conflicts is to make sure no two devices use the same interrupt. Serial port adapters are available for adding COM3 and COM4 serial ports that do not share the interrupts used by COM1 and COM2. These boards enable the new COM ports to use other normally available interrupts, such as IRQs 10, 11, 12, 15, and 5.

I never recommend configuring a system with shared ISA interrupts; it is a sure way to run into problems later. However, interrupts used by PCI boards can be shared if you use Windows 95 OSR 2.x, Windows 98, Windows Me, Windows 2000, or Windows XP with recent chipsets that support a feature called IRQ steering.

If you suspect an interrupt problem with a bus-type mouse, you can use the Device Manager built into Windows (which is accessible from the System control panel). The Device Manager in Windows 9x/Me/2000/XP is part of the Plug and Play (PnP) software for the system, and it is usually 100% accurate on PnP hardware.

Although some of these interrupt-reporting programs can have problems, most can easily identify the mouse IRQ if the mouse driver has been loaded. After the IRQ is identified, you might need to change the IRQ setting of the bus mouse adapter or one or more other devices in your system so that everything works together properly.

If your driver refuses to recognize the mouse at all, regardless of its type, try using a different mouse that you know works. Replacing a defective mouse with a known good one might be the only way to know whether the problem is indeed caused by a bad mouse.

I have had problems in which a bad mouse caused the system to lock right as the driver loaded or when third-party diagnostics were being run on the system. If you use a DOS-based diagnostic, such as Microsoft MSD or AMIDIAG, and the system locks up during the mouse test, you have found a problem with either the mouse or the mouse port.

Try replacing the mouse to see whether that helps. If it does not, you might need to replace the serial port or bus mouse adapter. If a motherboard-based mouse port goes bad, you can replace the entire motherboard—which is usually expensive—or you can just disable the motherboard mouse port via jumpers or the system BIOS setup program and install a serial mouse instead.

This method enables you to continue using the system without having to replace the motherboard. On systems with Windows 98/Me/2000/XP, you also can switch to a USB mouse, using USB ports on your motherboard or by installing a PCI-based USB card—provided your system has a USB port.

Driver Software

Most mice and other pointing devices in use today emulate a Microsoft mouse, enabling you to have basic two-button plus scrolling functions with current versions of Windows without loading any special drivers.

However, if your mouse has additional buttons or other special features, you will need to install device-specific drivers available from the mouse vendor. If you plan to use the mouse from a Windows 9x/Me command prompt or with DOS, you must load the driver manually.