What version Premiere Elements on your Windows 8.1 (assumed 64 bit) computer?
How is the mouse no longer working?
a. its cursor is frozen
b. its scroll wheel does not work?
c. Do you use a wired or non wired mouse?
Did you have a pen/mouse and tablet device, switched to mouse without setting its preferences?
Did you check the mouse under Control Panel/Device Manager/?
Let us start here and then decide what next based on the details in your reply.