I agree to try different ports, keyboard etc. For example, unplug EVERYTHING from USB except your keyboard. If you still get issues, simply unplug and try every USB port (no need to reboot. Takes up to 30 seconds to reconnect).
If you still get issues, try a different keyboard.
At this point, if you still have issues it's PROBABLY a motherboard hardware issue. There's a way to see if it's not a software issue.
Install Ubuntu either using WUBI (which can then uninstall Ubuntu after using the Add/Remove Programs), or simply BURN and BOOT to a CD or DVD.
If you don't have USB issues in Ubuntu, but do in Windows then you have a software issue. If so, reinstall your main motherboard chipset driver. You can also look at the Device Manager for CONFLICTS (black exclamation mark with yellow background).
So to simplify:
If motherboard is problem, sorry you'll need a new motherboard (or get an addon USB card and ONLY use it. Maybe that will work fine.)
If Windows is the problem (works in Ubuntu) you need to reinstall drivers or else reinstall Windows completely (backup any data etc first).
I should add that it's also possible that the problem is a defective POWER SUPPLY. Obviously you'd need to try with a different Power Supply that meets your systems needs.
This is a last resort.
*I saw a problem once that was actually due to RAM (complicated). It's a good idea to test your RAM anyway. Use the built-in test, or, better yet burn a USB or CD from www.memtest.org . (your BIOS must have the boot order set so that USB or CD/DVD comes before hard drive)