I've tried looking everywhere for a couple of days before opening a new thread here, but it seems there aren't any similar threads around.
In case I'm wrong please forgive me.

Description:
Changed the usb polling rate from 125 to 500 mhz,twice,using usbmrs 1.1.
Had no problems whatsoever the first time (roughly 9 months ago),and restored the old usbport.sys back to 125 'cause I didn't like it at first.

I changed it back to 500 again last week and,since then, only when I play Quake Live, the mouse randomly stops working every 3-4 minutes or so: it will turn off (= the sensor "light" disappears), and after 3-4 seconds it comes back to life.

When this happens I hear that windows sound you get when you plug/unplug something via usb.

I tried changing ports and unplugging/plugging the mouse again, but I get an error message about the installation of the device.
Tried restoring the usbport.sys file +doing again the usbmrs thing, problem persists.

OS: windows xp
mouse: mx518

Is there any chance to get it working without having to format?