It might be that the main OS partition's boot flag was set off. If that's the case, try the following to see if it fixes the problem:
Preferably from a clean computer, I need you to download:
gparted-live-0.10.0-3.isoCreate a bootable CD for Gparted from the ISO image. You can use
ImgBurn do this.
Now boot off of the newly created Gparted CD.

You should be here...
Press ENTER

By default, "do not touch keymap" is highlighted. Leave this setting alone and just press ENTER.

Choose your language and press ENTER. English is default [33]

Once again, at this prompt, press ENTER
You will now be taken to the main GUI screen below

Is "boot" next to your OS drive?
If "boot" is not next to your OS drive under "
Flags", right-mouse click the OS drive while in Gparted and select
Manage FlagsIn the menu that pops up, place a checkmark in
boot like the picture below:

Now
double-click the

button.
You should receive a small pop up like this:

Choose reboot and then press OK.
If the above doesn't work, there's one more method I have in mind.
Edited by Amlak, 10 May 2012 - 06:48 PM.