The above users are essentially correct. Without knowing specifics of your system, I'd have to advise you to check:
1. The battery if it's a wireless setup
2. Is it clean? Balls need to be taken out and cleaned with alcohol, be sure to get the little wheels the ball comes in contact with. If optical mouse, then check for dust or hair that are in the cavity where the LED or laser are
3. Did it work just fine for a while and then start malfunctioning, or is it a new install? if it worked fine it's probably not the drivers. If it's a new install, while mouse drivers do not often fail, if you have a specialty mouse I suppose it's possible.
4. is your system generally sluggish? Your hard drive could need defragmenting. It's good to perform an error check as well. Other causes of sluggish PC are spyware, adware, and malware. These install without your knowledge or consent so most people don't know they have them until a problem developes. That can cause the issue you describe.
Troubleshooting: I would try the mouse on another PC and see what it does. Also try another mouse on your computer and see what that does as well. If the problem follows the mouse, then you have a hardware problem and should try changing batteries, making sure the dip switches for wireless channel are set correctly, clean the mouse, etc..
If the issue stays with the computer no matter what mouse you use with it, then your issue is with the Computer. First defragment your hard drive. If that doesn't work start the computer in safe mode by pressing F8 on boot and selecting safe mode. This will load only essential components with non-vendor specific drivers. you will not be able to connect to the net unless you select safe mode with networking support. If the mouse works fine in safe mode, you know it's with a component windows didn't start. Check drivers at this point. If you frequently install and uninstall programs a registry cleaner might be in order.
If the mouse continues to malfunction suspect that a piece of software that you didn't want on your machine is causing the system to be sluggish. Take corrective action by running a virus scan with the latest deffinitions, download and run spybot search and destroy, adaware personal, windows deffender, a-squared, and other anti-spyware/anti-adware tools.
If all else fails...and the mouse isn't the only thing malfunctioning on the PC...it may be time to reload the OS. That's a drastic step, but that should be done every couple of years because windows gets bloated after years of use. Windows bloat can sometimes result in quirky issues. The issue might be a sign of a larger underlying problem. If your computer isn't as snappy as when you got it then something needs to be done to it.
If that fails...get a Mac