Ok Guys this is a tough one. About 2 months ago i started getting the "operating system not found" message when trying to boot a laptop. So with the unit being under warranty i had the Hard drive replaced. It worked great for about 2 weeks then got the same message again. So callend in service guys again this time they replaced the Motherboard and tested the Hard drive just in case. It was fine for about 2 weeks again, then yet again the message started coming up again, i have since given the user another laptop from our stores at the school and taken it upon myslef to work out the cause of this intermittent error from hell. I cannot for the life of me work out what is wrong. If anyone has any ideas please share them with me! Cheers