On the back of your system or tower case you will see the main I/O shield.
You will see a circular connection colored purple and green, above or bellow it you have two usb ports.
Connect both your mouse and keyboard to those two usb ports of the system.
Restart the system, and while booting press the assigned key on your keyboard to enter the bios setup menu of the motherboard.
If the board is new and is UEFI capable, look for an advanced bios or settings mode option for the bios.
In the advanced menu options you will find the options to enable or disable use of each of the provided usb ports on your motherboard.
Enable them.
Then save the new changes you made before you exit the bios setup options.
To load windows 7 in safe mode...