Sorry guys, I know I'm late to report what happened after I ask your help, but I've been away for some time. Fortunately my FSX problem was solved. My old HDD was (and is) OK and now my FS is working fine again. It wasn't a hardware fault, the problem occurred during a W7 scheduled update. It wasn't necessary to format the HDD; just using a W7 repair tool. I'm a happy man again. ;D

Thank you all for the ideas to fix it.