Posted 21 July 2010 - 04:54 PM
I think your premises...are awry.
Error loading operating system...can mean various things. It's an indication that something is wrong with the partition, the drive, the boot structure, or the boot option settings (generally speaking).
When a hard drive which has been formatted...is seen as a drive which is not formatted...that's usually an indication that the file system (NTFS) has a problem. The problem could be caused by the structure of the hard drive or the file system could be damaged or other key system files could be damaged...the result is that the partition can no longer be recognized by the system. Hence, a user may receive messages indicating that the hard drive needs to be formatted and has no recognized partition.
All of this has nothing to do with a virus scan...it happens routinely enough that it's well documented, if not understood.
You can try data-recovery software to see if it is able to see files on the drive. If so, I suggest moving any value files...before attempting any trouble-shooting on the drive.