Slow transfer with memory stick (819 kb/s)
First step is to check if the device has suddenly become USB 1.1 instead of 2.
This is explained with screen captures in Checking for USB 2, but in a nutshell, open Device Manager and check if under "Universal Serial Bus controllers" you have "ENHANCED USB Host Controller".
Also check in the BIOS, if USB 2 is suddenly turned off.
Other thing to try is re-installing the PCI to USB host controller driver.
It's also possible (but unlikely) that the USB device has become highly fragmented, which can be fixed by a reformatting.