F'ed USB ports or not enough power?

Just a really quick question...

Just a hour or two before I installed a new internal HD. As I was booting up my computer, everything was working fine and all but then as I was about to punch in my password and crap, my keyboard didn't work. It lights up and all but it didn't respond to any keys. My mouse also died.

So, I unplugged and replugged them plus tried all other USB ports. No use and this time they're dead and with the keyboard doing the same thing as before, from time to time.

So, I killed the power and rebooted. They worked but the keyboard went  on and off for a little bit. Lastly, when I remove any of the USB connections and reconnect them. They will not work but they will work if left untouched.

So I have to ask, is it my USB ports or my power supply not supplying enough power at times?

And if you're wondering, I tried using my stuff on other computers and they worked perfectly, so its not the stuff. It should be one of those two.

So what is it?

You don't understand how power supplies work.
Your USB ports are fucked.

But they're working now.

Pretty strange. Eh.
As long as they work, I'll be fine.

Meh, USB...