两种可能：
1. 鼠标坏了

2. 10.9升到10.10 会有几率系统顿卡的 解决方法是安全模式下 进行一次验证磁盘权限 一次修复 然后重置System Management Controller 最后重置PRAM  系统立马恢复到10.9.5 那丝般顺滑的感觉了

A small amount of your computer’s memory, called “parameter random-access memory” or PRAM, stores certain settings in a location that OS X can access quickly. The particular settings that are stored depend on your type of Mac and the types of devices connected to it. The settings include your designated startup disk, display resolution, speaker volume, and other information.

Note: To print these instructions, open Help Viewer’s Action pop-up menu (looks like a gear), then choose Print.
Shut down your Mac.
Locate the following keys on the keyboard: Option, Command (⌘, P, and R. You will need to hold these keys down simultaneously in step 4.
Turn on your Mac.
Immediately press and hold the Option-Command-P-R keys. You must press this key combination before the gray screen appears.
Continue holding the keys down until your Mac restarts, and you hear the startup sound for the second time.

Release the keys.
Resetting PRAM may change some system settings and preferences. Use System Preferences to restore your settings.