To fix a mouse that drags, try the following: Make sure you're using a mouse designed for a desktop computer (not a trackball or a laptop touch pad). Make sure there is no dust or dirt in the mouse or the mouse pad. Dust or dirt can cause drag. Try cleaning the mouse. Try cleaning the mouse pad.
The simplest way to fix this is to go to Control Panel and click on Mouse. Then, go to the Pointer Options tab and turn off the Enhance Pointer Precision option.