Your USB power might be failing because there are too many devices. Try plugging them into a different place; you might have to try several ports before you find a configuration that works or even makes the situation better. Also, if you are using a USB hub disconnect it from there.
To see if this is really the problem, open up a terminal, then when the mouse fails, type in
lsusb and see if the mouse appears in the list. If the mouse has disappeared then lack of USB power is likely your problem.
A USB mouse can actually take up much power compared to other devices, and you might want to find a substitute. But if you have other high-powered devices, you can try unplugging them. If unplugging other USB devices from the PC helps, then you will have to find substitutes for them.