rt2500usb.sys is a Ralink driver file.
Ralink makes wireless chipsets (so do Atheros and Broadcom), and is probably what's used in your Linksys wireless adapter.
You should try finding a new driver for your wireless card; I would suggest finding one from Ralink directly, instead of Linksys.
go to this
click on USB (RT2500USB)
you don't have to put in a name or email, just click accept.
Then install this driver using device manager.