I think it has to be the right one. Try one and if it does not boot....use the other one. Mine had two also but one said "USB 2.0" so I used that one....worked fine.
System Manufacturer/Model Number Keeps changing - (Custom) OS Windows 7 Professional x64 CPU Intel Core i7 860 Motherboard Gigabyte GA-P55-UD4P Memory 4GB DDR3 Mushkin 1600Mhz @ 7-8-7-20 Graphics Card MSI GTS250 1GB DDR3 Twin Frozr Sound Card Onboard realtek Monitor(s) Displays Samsung SyncMaster 24" P2450 + Samsung 20" 2033 Screen Resolution 1920 X 1080 and 1600 X 900 (#2 system 1440 X 900)
Keyboard Gigabyte USB keyboard Mouse Microsoft wireless laser mouse 5000 PSU Corsair 750 HX Modular Case Lancool PC-K62 Cooling Cooler Master TX3 CPU cooler and 4-140mm and 1-120mm case Hard Drives Patriot Inferno 120GB SSD + 3 WD Blue 640GB drives Internet Speed 7 Mb down 1.5 up Other Info System #2: AMD Phenom II X6 1055T (Freezer 7 Pro cooler) - Gigabyte 880GMA-UD2H - WD 500GB Black - 9500GT (1GB) 500W OCZ modular PSU - Antec 200 case. System #3 (LapTop) Core 2 Duo T6670 - 320GB 7200RPM HD - 4GB DDR3 RAM.
It has to be before anything else that has an OS on it. Can be first or second, but it must be before the hard drive, else the OS on the hard drive will load before the USB is tried.