You are missing at least one critical OS file.
FREE and TOTALY legal option: Install Linux. Most distributions are available for free.
Backup your data before installing.
In this case, I recomend reformating using the native file system. If you reformat, you MUST ABSOLUTELY backup ALL data BEFORE going further.
GRAY but free option: Download a copy of the installed OS and burn it to a CD (or DVD if Windows Vista or 7).
Boot from that disk and during the install process, sellect "Update", or "Repair" if update is not offered (Windows XP).
To stay legal, you MUST use the SAME Windows version as the one that is actualy installed.
The update option will replace all the OS files but leave your data and settings intact. This option ASSUME that you have a valid copy already installed and automaticaly use your actual registration key. If the found OS is the same version, it assume that it have been damaged and will repair it. Your installed applications will STAY installed. You'll need to get all published updates from Microsoft.
The repair option is NOT safe for your data if they are located on the same partition as the OS. BACK UP your data BEFORE proceeding!!! Your settings will NOT be preserved. You will probably need to reinstall most applications.
"mm", messing with the registry CAN'T cause the "No operating system found" message. That message is generated BEFORE you even ATTEMPT to access the registry, or if the registry FILE containing the HKLM section itself is missing (it's impossible under almost any conditions as that file is ALWAYS in use and locked).
Electro, August 2012
