You haven't given us any details about your PC (motherboard, keyboard, mouse make and model). You can edit your question to include the specs.
Meanwhile I have two solutions you may try. None of them do anything bad to your system.
This may seem counter-intuitive but Windows 7's USB stack is fully operational during setup. It will detect USB device insertions and removals.
Knowing this, you can overcome possible BIOS USB bugs by booting into Windows seutp exactly as you did, wait until the choose language screen appears, then without turning the computer off or rebooting unplug the keyboard and mouse and plug them back into different USB ports. This trick has worked for me in the past.
You may need to adjust some settings in your BIOS. Your motherboard manual will have instructions on how to enter BIOS setup.
When you get into BIOS setup, trawl through all the various menus and sub-menus and try find the following options. They might not read exactly as I've written them but you'll spot them if they're there.
Windows 7 has no need for BIOS legacy support, in fact it can interfere sometimes, so set these options:
- Legacy USB = Disabled
- EHCI Pre-Boot Driver = Disabled
- XHCI Pre-Boot Driver = Disabled
Also make sure USB2 support is enabled, if the option exists:
Or if the above option doesn't exist, make sure USB 3.0 is switchable:
- XHCI/USB 3.0 Switchable = Enabled
Also set these options if you have them, this adjusts how BIOS hands over the USB controller to the OS when it needs it:
- EHCI/USB 2.0 hand-off = Disabled
- XHCI/USB 3.0 hand-off = Enabled
Make sure you save the settings before exiting BIOS setup.
As you pointed out yourself do use USB 2.0 ports if you have them. Good luck and let us know how you go :-)
Update: If you are using a newer Intel processor with USB 3.0 you might have to add the USB 3.0 drivers to the installation image. You can do this the hard way using the Windows DSIM utility but Intel also distributes a tool to automate the process. More info is on Intel's website.