Answer:Mouse is not working because you haven't changed your battery for months.
Remember that, most of wireless mouses use AA 1.5V battery for it's power on. If you've let your computer and mouse set on, then the battery can only run around 5-6 months. If you turn off your mouse everytime you're not using then the battery life might get longer. So, all you have to do is buy new batteries and replace it. Follow steps of replacing battery in this video.
(Consider buying dry battery for using longer)
No.2: Loose battery in the tray
This is quite common as well. We understand that the mouse made materials can have its own changing. Sometimes, you might drop your mouse, then after that, the loosen battery just happening around. A loosen battery might get your wireless mouse not working well. It works then stop at the middle. Follow the easy steps to fix this state of mouse is not working.
No. 3: Bad Pairing.
Due to some reasons, bad pairing can happen and get your mouse stuck on laptop screen. Bad pairing might be from overworking or overloading tasks on your PC. Easy quick fix for bad pairing is disconnect your USB receiver for a while and re-plug in later on.
No.4: On/Off Switch or Power button on the mouse just drop or loosen in
Many people might have problems with their mouse on/off switch button. Don't worry, this can be fixed as well. You can open the mouse (just look under the battery, there is a single screw). Open the mouse from this screw, and disassembly it carefully. You can see the on/off switch is just around the corner. Now, you can, reattach the button and close the mouse correctly.
No. 5 : Buy a new mouse
I've suggested a way to search for a new wireless mouse with USB Unifying Receiver. For a wireless mouse that allows Unifiying receiver, then you don't worry when your current usb receiver get lost (because, you can always buy a new usb receiver).
Explanation: