Computer just did something strange.

[Jason1]

My Computer just did something very strange that has me a little worried. I was just browsing the web casually when, all of a sudden, my tower made the sort of "Click" sound that it makes when it goes into sleep mode. But I didnt put it in sleep mode, and instead of just making the sound once, it made it many times, probably close to 10, then locked up the computer. I pushed the reset button, and it said something about a failure on boot up, insert boot disk and press any key. I tried pushing reset again and got the same thing. So then I held down the power button to turn the system off entirely, then turned it back on and it loaded up fine. Scared me though.

Any idea what it might have been, and should I be worried?