Hiya I recently set up a new core i7 system I'm using a gigabyte p55-ud2 motherboard. I plugged my usb keyboard and mouse into 2 usb's and attempted to install windows 7 but when it asks me to press any button to boot into it the usb keyboard does not work. I can use it to get into the BIOS. I looked in there but there is no usb keyboard and mouse option like my last mobo, usb conyroller, usb storage controller and legacy usb controller are all set to enabled but no joy. I also tried with legacy off. I can get into the windows 7 dvd with my ps/2 keyboard and they both work but I need them working before the os is loaded because I use grub.
Gigabyte just released a bunch of new BIOS updates for their P55 boards. I have heard from someone with the UD3R that it fixed some USB issues they were having. Worth a shot for you.
If you have revision 1.0, the BIOS can be found here: http://www.gigabyte.us/Support/Motherboard/BIOS_Model.a...
EDIT: I did a little more research. I would still advice updating your BIOS. However I also found that some motherboards just don't allow what you're trying to do. Some do, but not in all USB ports so you may have to try them all. Start with the ones on the back plate. Also, some suggest enabling the USB Legacy function. According to your manual this "Allows USB keyboard to be used in MS-DOS."
What other devices do you have currently plugged into your machine aside from your mouse and keyboard? Has Windows 7 attempted to install "new devices" if and when you have both your PS/2 keyboard and mouse and USB keyboard and mouse connected simultaneously?
Also, have you installed the latest chipset drivers for your motherboard?
Should you require additional assistance and feedback, Microsoft does have an official Windows 7 Support Forum located here http://tinyurl.com/9fhdl5 . It is supported by product specialists as well as engineers and support teams.