yohannes, there should be a hidden recovery partition that allows you to recover your OS. Disable boot booster in the BIOS before system recovery. Reboot the computer, press F2 to show POST and press F2 again to enter BIOS setup. Arrow to the BOOT tab displayed on screen set Boot booster to disabled. F10 to exit and save. Now reboot and Press F9 during bootup, check the mark button to start system recovery and follow the onscreen prompts. After that re-enable boot booster in BIOS afterwards. this of course only works if you have the original HDD and if the drive is still physically okay. If the drive is not being recognized or has some internal damage, this will not work. then you will have to replace the drive and reinstall the OS through a USB drive. Hope this helps, good luck.