This happens when i turned on my pc and i have to press a key so i can start up. This is a bit scary, i freaked not knowing that it wouldn't startup. I looked Microsoft's official site for solutions but i guess i need a windows CD which i don't have.
If SMART is enabled, get a copy of ubuntu 10.04 and boot into the cd. Then on the Live OS, go to on the of the screen, "System", "Preferences", "Disk Utility".
Then a program should open up and click on your HDD or the left. Then click on the button that says "Check Smart Status." This will tell if you have any bad sectors. I usually run the short HDD test and it is pretty accurate.