Assistance - "Error Loading Operating System"

Hey everyone here at Tom's Hardware.

I am in need of a assistance with a problem I am currently having with my computer.

Here's the story:

I went to a LAN and we played all day and shared a lot of files. At a point, while everyone we're copying files from my pc, I simultaneously started Crysis and played, but it, as expected, lagged and I quitted the game and it freezed a bit and I was forced to use task manager to kill the process.
Anyway when I got back to the desktop everything was very slow and I had no choice but to reset my pc. After I pushed the reset button the instead of booting the pc gave me the following message:

"Error Loading Operating System"

My friend helped me by getting a Windows XP cd and repairing my windows and then the pc booted up fine and everything was as fast and perfect as always.

When I got home, I turned my pc on again and the message was back,
can someone provide some advice for me, please?    



Windows XP Service Pack 2