I suggest Uninstalling the Driver from Device Manager And/or Programs and Features. Then going to another computer and download the latest driver available from realtek. Copy these to a USB Drive, then Back to your computer. and Install (MOVE THE FILE TO THE DESKTOP, DO NOT INSTALL FROM USB DRIVE)
Id also try other USB Ports. And If your using a USB Hub, use a port that goes directly to your system
Hope Ive been helpful in some way =D
Ive seen so many problems with USB Wifi. I generally only recommend PCI-E Based Solutions. Should you go this route, I recommend the TP-Link WDN3800 N600 Dual Band (Im assuming were talking about a desktop)..... Just dont install the Utility for it, Only the driver