What is the full model number or product number of your PC?
The product number can be found on the same sticker as the serial number.
The USB KB and mouse quit working during the W7 install because the W7 installation disk does not have the required USB 3 drivers needed, and the PC does not have native USB 2 support until after W7 is installed and you install the chipset driver.
If your PC has the Intel Skylake chipset, then you need to run this tool to put the USB 3 drivers into your W7 installation flash drive.
If you are using a DVD, you will need to convert that to a W7 installation flash drive.
There is a readme link for how to use the tool, and additional instructions for converting the DVD into a USB installation flash drive.
Select the file for the version of Windows you plan to run the tool on.