USB keyboard and mouse refuse to work

Someone please help me, I can’t seem to find any solutions for this…

Recently I re-installed Windows XP Pro due to some trojan infection. I decided to install Service Pack 2 again, and after the installation, I restarted my computer. But now my keyboard and mouse don’t work. The lights on my mouse and keyboard light up for about 1 second upon starting up of my pc but they die off really fast. I can’t even press on F8 to get into safe mode.

I’m totally not an expert in computers so someone please enlighten me on this….